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.
Variations of the word: Adrahil, Agrahil.