AZ-ZAHIR/ADH-DHAAHIR MEANING - 99 NAMES OF ALLAH:

Arabic Root:
From the root za-ha-ra (ظ ه ر), which has the following classical Arabic connotations: to be visible, manifest, obvious, clear, distinct, to open, to come out, to cause, to appear after being concealed, to be conspicuous, distinct, to ascend, mount, have higher status, to have the upper hand, subdue, overcome, to endorse, help, aid, support others, render superior.

Mentioning the names together is necessary for this pair because to say Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is hidden by itself can imply a negative connotation. In Surah Hadid, there is one short ayah which mentions four of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ divine names.

Huwal Awwalu wal’Aakhiru waz Zaahiru wal Baatinu wa huwa bikulli shai’in Aleem

The four names in this verse are best viewed in pairs for their connected meaning. The first pairing is Al-Awwal and Al-Akhir (The First and The Last). The following two names which will be the focus of this section are Az-Zahir and Al-Batin (The Manifest, The Hidden). We included three different translations of this ayah to help us see understand the nuances.

A pairing paradox:
At first, the pairing of Al-Zahir and Al-Batin seems contradictory. How can something be both manifest yet hidden? One interpretation is He is outwardly manifested, all that exists serves as clear proof of His manifestation, as well as His knowledge and His power. But He is hidden in plain sight, He appears before everything, and it should be apparent, but they ignore the truth presented right in front of them. Another view of Al-Zahir that is also reflected in the translations is that He is transcendent above all, predominating over them. He is High above, a clear witness over everything, and He knows all which is concealed or hidden. He is fully acquainted with His servants and knows their inner dimensions.

Imam Ghazali mentions these two attributes that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is manifest and hidden, referring to the mode of perception. If you need to "see it to believe it," you will surely miss Him. But if you find the ways in which He manifests Himself through the Prophets (may peace be upon them), His books, religion, power, knowledge, and all the ways He's supplied blessings for you, you will surely find Him. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is "hidden when He is sought by sensory perception or using the resources of imagination, yet manifest when sought by way of inference using the resources of reason."

Laa tudrikuhul absaaru wa Huwa yudrikul absaara wa huwal Lateeful Khabeer

English Translation:
"Vision perceives Him not, but He perceives [all] vision; and He is the Subtle, the Acquainted." — (Qur'an 6:103)

Seeing Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ:
This is also a topic of discussion Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ had with Musa (as) as captured in the Qur'an. Musa (as) is the only person we know to have communicated directly with Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. In his conversation, he asked if the veil which separates God from us could be lifted so that he may see Him. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ told Musa (as) He cannot be seen and then demonstrated why by revealing Himself to a nearby mountain. Upon doing so, the mountain turned to ashes/dust and was leveled. The whole experience caused Musa (as) to collapse unconscious.

Wa lammaa jaaa’a Moosa limeeqaatinaa wa kallamahoo Rabbuhoo qaala Rabbi arineee anzur ilaik; qaala lan taraanee wa laakininzur ilal jabali fa inistaqarra makaanahoo fasawfa taraanee; falammaa tajallaa Rabbuhoo liljabali ja’alahoo dakkanw wa kharra Moosaa sa’iqaa; falammaaa afaaqa qaala Subhaanaka tubtu ilaika wa ana awwalul mu’mineen

English Translation:
"And when Moses arrived at Our appointed time and his Lord spoke to him, he said, 'My Lord, show me [Yourself] that I may look at You.' [Allah] said, “You will not see Me, but look at the mountain; if it should remain in place, then you will see Me.” But when his Lord appeared to the mountain, He rendered it level, and Moses fell unconscious. And when he awoke, he said, 'Exalted are You! I have repented to You, and I am the first of the believers.'" — (Qur'an 7:143)

Wa maa kaana libasharin any yukallimahul laahu illaa wahyan aw minw waraaa’i hijaabin aw yursila Rasoolan fa yoohiya bi iznihee maa yashaaa’; innahoo ‘Aliyyun Hakeem

English Translation:
"And it is not for any human being that Allah should speak to him except by revelation or from behind a partition or that He sends a messenger to reveal, by His permission, what He wills. Indeed, He is Most High and Wise." — (Qur'an 42:51)

Al-Ghazali gives an illustrative example of how, if you read a page of a book, would you doubt that the author exists? Or would you recognize the author's existence for the book to exist? We could go one step further and infer from what was written that they were knowledgeable and assume they had the qualities of sight and hearing. ^[1] Now, if you take a second to ponder the arrangement of the universe. See all its perfectly managed complexity. Why do you need to see the organizer to validate His existence? The creation and perfect arrangement of all the atoms and molecules, everything around us, is a clear manifest proof of His existence. It speaks volumes about all of His glorious attributes. Even we can see the wisdom in His book, Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ had authored all of creation, kun fa-yakoon, "'Be', and it is!" (Qur'an 36:82). This also brings us back to the first pairing we mentioned (Al-Awwal and Al-Akhir), recognizing Him as the originator or the source for all creation.

It was narrated from Umar that Jibreel عليه السلام said to the Prophet ﷺ: What is faith (iman)? He said: “To believe in Allah, His Angels, His Books, His Messengers, the Last Day and the divine decree, both good and bad,” Jibreel said to him: You have spoken the truth. He said: We were amazed that he asked him and then confirmed his answers as being correct. The Prophet ﷺ said: "That was Jībreel, who came to teach you your religion.`" ^[2]

It is also worth mentioning that Surah Al-An'am ayah 120 notes two Arabic words, zaahiral and baatinah, but not in the context of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ glorious names. Rather, these words were a message to the believers about what is permissible and forbidden. It gives clear guidance to avoid sinning, whether open (zaahiral) or hidden (baatinah).

Wa zaroo zaahiral ismi wa baatinah; innal lazeena yaksiboonal ismaa sa yujzawna bimaa kaanoo yaqtarifoon

ABDEL HALEEM TRANSLATION:
"Avoid committing sin, whether openly or in secret, for those who commit sin will be repaid for what they do," — (Qur'an 6:120)

Du'a of Prophet Muhammad ﷺ:
There is also mention of these two names as recorded in a du'a of Prophet Muhammad ﷺ:

Allahumma Rabbas-samawati wa Rabbal-ardi, wa Rabbul-'Arshil-'Azim, Rabbana wa Rabba kulli shay, faliqal-habbi wan-nawa, wa munzilat-Tawrati wal-Injili wal-furqan. A'udhu bika min sharri kulli shayin 'anta akhidhun binasiyatih, alllahumma 'ant al'awwal falays qablaka shaay' wa'antal akhiru falaysa baadika shayy, Antaz-zahiru, fa laysa fawqaka shay’, wa antal-batinu fa laysa dunaka shay, aqdi 'annid-dayna waghnini minal-faqr

Suhail reported that Abu Salih used to command us (in these words): When any one of you intends to go to sleep, he should lie on the bed on his right side and then say: "O Allah. the Lord of the Heavens and the Lord of the Earth and Lord of the Magnificent Throne, our Lord, and the Lord of everything, the Splitter of the grain of corn and the datestone (or fruit kernal), the Revealer of Torah and Injil (Bible) and Criterion (the Holy Qur'an), I seek refuge in Thee from the evil of every - thing Thou art to sieze by the forelock (Thou hast perfect control over it). O Allah, Thou art the First, there is naught before Thee, and Thou art the Last and there is naught after Thee, and Thou art Evident and there is nothing above Thee, and Thou art Innermost and there is nothing beyond Thee. Remove the burden of debt from us and relieve us from want." Abu Salih used to narrate it from Abu Huraira who narrated it from Allah's Apostle (ﷺ). ^[3]

References:
[1] Imam al Ghazali was an 11th-century author and philosopher. Keep in mind the context; braille was invented in 1824, and sign-language in the 17th century. The modern accessibility tools we take for granted today did not exist. So, the analogy made must be viewed in context.
[2] Sahih (Darussalam) Musnad Ahmad 191
[3] Sahih Muslim 2713a