Amarantha is a rare botanical name whose mythical equivalent was believed to be immortal.  The Italian and Spanish form is the somewhat-more-acccessible Amaranta.

Amarantha

Amargo

Ambrogio

Ambroise

Gentle but grandiose and beloved by British novelists including Evelyn Waugh and P. G. Wodehouse, Ambrose was a fast rising name in 2022. Entering the UK Top 1000 for the first time and proving popular among Nameberry users, its elegance, softness, and vintage style means it fits in with popular Theodore, Sebastian, and Jeremiah. 
 With an air of blooming well-being, Ambrose feels a bit upper-class, a little posh, but not too stuffy. It comes from the same Greek root as 'ambrosia', the food of the gods, said to confer immortality.
 Ambrose was the name of one of the important doctors of the early Christian church, the fourth century St. Ambrose. It also belonged to one of the four great Latin teachers of Christianity, who also developed the use of music in church services. TV fanatics might be interested to know that in 1961, Ambrose was designated the patron saint of educational television by Pope John XXII.
 One thing that might given some parents pause is the problem of finding a nickname for the stately Ambrose. Ami? Bro? Amby? They might work for some, but other options include the stylish Bo, the literary Bram, the sweet Ro, or even the unexpected and unisex Rose.

Ambrose

Ambrosi

Ambrosia combines some of the more whimsical qualities of more popular Aurora and Isabella, with a heavenly meaning. 

In Greek mythology, Ambrosia was not a goddess or other figure but literally the food and drink of the gods, said to confer immortality. The Ancient Greek word ambrosios, meaning immortal, gave rise to the Latin name Ambrosius, which became the modern Ambrose.

Only a dozen baby girls were named Ambrosia in the US in the most recent year counted.

Ambrosia

Ambrosio

Ambrosius

Ambrus

A mouthful of a given name, but one that is common in its native Greece. Athanasius is the spelling Americans are more familiar with — St. Athanasius of Alexandria is considered one of the founders of Eastern Orthodox Christianity.

Athanasios

Aeturnus 

Afanasiy 

Afanasy 

Aina 

Aive 

Aivi 

Alecto 

Alekto 

Amar

Amaranth

Amaranthine 

Ambrogino 

Ambroos

Ambrosina 

Ambrosine

Ambrosios 

Ambrózia 

Ameretat 

Amordad 

Amrit

Amrita

Amurdad

Ananta 

Ananth 

Anantha 

Arius 

AtAnas

AtAnasija 

AtAnasije

Atanase

Atanasij

Athanas 

Athanasia

Athanasius 

Baki

Baqi

Dari

EDERn

Elam is the name of no fewer than eight Old Testament figures. The most notable was a grandson of Noah whose followers were dubbed the Elamites. Elam is commonly used in Amish communities today.

Elam

If you're looking for a Welsh name less common than Dylan, Griffin, Evan, or Morgan, you might want to consider this offbeat epithet of the wise wizard Merlin. 

Root name Ambrose is an ancient saints' name derived from the Greek ambrosia, the food and drink of the gods that conferred immortality.

Emrys

Eliad

Evermore

Forever

Halide

Halit

Heng

Javaid 

Javed 

Khalid has flirted with the Top 1000 for several decades now, climbing back on in 2015 after more than a decade's absence. Its return could be in part because of the popularity of snapchat personality and rap collaborator DJ Khaled. R&B singer Khalid may also be contributing to its newfound popularity.  The name is important in Islamic history thanks to a 7th century military leader. Khalida is the feminine version.

Khalid

Khalida is an evocative Middle Eastern choice.  Its male counterpart, Khalid, recently returned to the US Top 1000.

Khalida

Khaled 

Lestari

Ludari 

Mordad

Nithya 

Nitya

Oziah

Ozian

Ozion

Ozius

A 3rd century saint's name sometimes used in Catholic communities, and in Western European countries like Portugal and Italy. 

Perpetua

Samad

Samed

Semper

Thanasis

Thanos originated as a short form of Athanasios, a Greek name meaning "immortal." It is composed of the elements a, a negative Greek prefix, and thanatos, meaning "death." St. Athanasius, who used the Latin spelling of the name, was a bishop of Alexandria and known for his opposition to Arianism.
 
Though this is a perfectly respectable Greek choice, be aware that Thanos the Mad Titan is a sinister Marvel Comics villain.

Thanos

Tase 

Yong

Zyanya 

Vana's list "Immortal, Eternal and Forever Names" of 80 great name ideas: Amarantha - Zyanya !

Immortal, Eternal and Forever Names

Names that mean immortal, eternal or forever