Fifth king of Arnor (LotR/1038), his name seems to be a compound of aran “king” and the affix -tar “high; lord”. As such, his name might mean “✱High King”, perhaps an allusion to the claim of his house over the thrones of both Gondor and Arnor.
masculine name. *High King
Word Gloss aran “king” tar- “high, high; [ᴹQ.] king or queen (in compounds)”