Greek sea-nymph, wife of Poseidon; the first element appears to be amphi "round about, on both sides, all around" (see amphi-), the second trite, fem of tritos "third," but the sense intended by the compound is unclear.
Entries linking to amphitrite
amphi-
before a vowel amph-, word-forming element meaning "on both sides, of both kinds; on all sides, all around," from Greek amphi (prep., adv.) "round about, on both sides of, all around; about, regarding," which is cognate with Latin ambi-, both from PIE root *ambhi- "around."