loquacious (adj.) 1660s, a back-formation from loquacity, or else formed from stem of Latin loquax (genitive loquacis) "talkative," from loqui "to speak" (from PIE root *tolkw- "to speak") + -ous. Compare French loquace, Spanish locuaz. Related: Loquaciously; loquaciousness.
talkative (adj.) early 15c.; see talk (v.) + -ative. An early hybrid word in English. Originally especially "boastful," but now considered less pejorative than loquacious or garrulous. Related: Talkatively; talkativeness.