Potent, a.
Etymology: [L. potens, -entis, p. pr. of posse to be able, to have power, fr. potis able, capable (akin to Skr. pati master, lord) + esse to be. See Host a landlord, Am, and cf. Despot, Podesta, Possible, Power, Puissant.]
1. Producing great physical effects; forcible; powerful' efficacious; as, a potent medicine. "Harsh and potent injuries." Shak. Moses once more his potent rod extends. Milton.
2. Having great authority, control, or dominion; puissant; mighty; influential; as, a potent prince. "A potent dukedom." Shak. Most potent, grave, and reverend signiors. Shak.
3. Powerful, in an intellectual or moral sense; having great influence; as, potent interest; a potent argument. Cross potent. (Her.) See Illust. (7) of Cross.
Syn. -- Powerful; mighty; puissant; strong; able; efficient; forcible; efficacious; cogent; influential.
1 other Webster entry under this spelling
Potent, n.
1. A prince; a potentate. [Obs.] Shak.
2. Etym: [See Potence.]
A staff or crutch. [Obs.]
3. (Her.)
One of the furs; a surface composed of patches which are supposed to represent crutch heads; they are always alternately argent and azure, unless otherwise specially mentioned. Counter potent (Her.), a fur differing from potent in the arrangement of the patches.
Shades of meaning
Fernald lists potent only as an antonym, under vain.
He lists it without comment; the entries above explain its neighbors.