tomfool

[Tom (nickname of Thomas) + FOOL.]

noun

One deficient in judgment and good sense: ass, fool, idiot, imbecile, jackass, mooncalf, moron, nincompoop, ninny, nitwit, simple, simpleton, softhead. Informal dope, gander, goose. Slang cretin, ding-dong, dip, goof, jerk, nerd, schmo, schmuck, turkey. See ability/inability.

adjective

So senseless as to be laughable: absurd, foolish, harebrained, idiotic, imbecilic, insane, lunatic, mad, moronic, nonsensical, preposterous, silly, softheaded, unearthly, zany. Informal cockeyed, crazy, loony, loopy. Slang balmy², dippy, dopey, jerky, sappy, wacky. See ability/inability, knowledge/ignorance.

The noun has one meaning:

Meaning #1: a person who lacks good judgment
  Synonyms: fool, sap, saphead, muggins

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