Adrahil presumably is an Adûnaic name of unknown meaning. The second element -hil (also seen in the name Imrahil) perhaps is related to the Westron ending -kil (cf. banakil, Tarkil) meaning "man", ultimately related to Elvish "follower".
Adûnaic
adrahil
masculine name. Adrahil
Adrahil II
Adrahil II
There were two men with this name in Tolkien’s legendarium. Adrahil I was a Gondorian prince who fought with King Ondoher against the Wainriders (UT/293-4, 319 note #39). Adrahil II was the 21st prince of Dol Amroth and the father of Imrahil (LotR/1056, PM/223). Since Tolkien said that “Imrahil is a Númenórean name” (LotR/1113), it is likely Adrahil was also Adûnaic. It seems that Adûnaic names were traditional for the princes of Dol Amroth: many of the known names (such as Adrahil, Imrahil and Imrazôr) are Adûnaic in form. It is not clear what the elements of these names might mean, however.
Conceptual Development: In the drafts of the Lord of the Rings appendices, Tolkien listed Adrahil as a Lemberin (Nandorin) name, along with Imrahil (PM/36). Probably when Imrahil became Adûnaic, Adrahil switched languages as well.