franticyoudaoicibaDictYouDict[frantic 词源字典]
frantic: [14] Frantic comes via Old French frenetique and Latin phreneticus from late Greek phrenētikús, a derivative of phrenítis ‘delirium’. This in turn was based on Greek phrén ‘mind’ (source also of English phrenology ‘study of cranial bumps to determine intelligence, character, etc’ [19]). The Old French form split into two virtually distinct words once English got hold of it: in one, the French three-syllable form was preserved, and even partially remodelled on its Latin ancestor, to give what has become modern English phrenetic, while in the other it was reduced to frentik which, for reasons that have never been satisfactorily explained, subsequently became frantic.

The related noun frenzy [14] retains the original vowel.
=> frenzy, phrenology[frantic etymology, frantic origin, 英语词源]
frantic (adj.)youdaoicibaDictYouDict
mid-14c., "insane," unexplained variant of Middle English frentik (see frenetic). Compare franzy, dialectal form of frenzy. Transferred meaning "affected by wild excitement" is from late 15c. Of the adverbial forms, frantically (1749) is later than franticly (1540s).