Synonyms for Eccentric:

adj.

absurd (adjective)
bizarre, implausible, invalid, self-contradictory, fallacious, farcical, irrational, inconsistent, senseless, inane, paradoxical, outlandish, impossible, illogical, ridiculous, nonsensical, preposterous, idiotic, ludicrous, foolish, crazy, contradictory, silly, incongruous, meaningless, absurd, anachronistic.
bizarre, unusual (adjective)
freakish, outlandish, strange, curious, idiosyncratic, odd, capricious, funny, abnormal, singular, crazy, erratic, uncommon, unnatural, kooky, irregular, unconventional, anomalous, bizarre, flaky, off-center, weird, oddball, aberrant, peculiar, quirky.
irregular (adjective)
inconstant, fitful, irregular, fluctuating, capricious, unrhythmical, sporadic, jerky, quirky, desultory, unsystematic, variable, intermittent, erratic, asymmetric, uneven.
nonconforming (adjective)
crazy, atypical, nonconforming, aberrant, funny, fey, singular, outlandish, bizarre, misfit, uncustomary, irregular, peculiar, oddball, deviant, crosspatch, uncommon, incongruous, mismatch, idiosyncratic, off, un-ordinary, curious, novel, abnormal, unfamiliar, exceptional, untypical, out of the ordinary, quirky, divergent, unusual, improper, strange, anomalous, oddity, unique, inconsistent, incompatible, deranged, erratic, unconventional, different, odd, extraordinary, freakish.
ridiculous (adjective)
weird, silly, oddball, comical, laughable, crazy, poppycock, absurd, outrageous, nonsensical, ludicrous, ridiculous, farcical, dubious, foolish, preposterous, bizarre, grotesque, incredible, outlandish, curious.

n.

mad, over-the-top, not in your right mind/not right in the head, insane, childish. madwoman, nutjob, maniac, madman, headcase, space cadet, lunatic. eccentric (noun)
freakish, flaky, bizarre, oddball, freaky, off-centered, nonconcentric, eccentric person, outre, case, off-center, unconventional, acentric, type, outlandish, character, geek.
person (noun)
eccentric person, geek, case, type, character, oddball.
person who is bizarre, unusual (noun)
character, oddity.

Other synonyms:

space cadet, surreal, kooky, nutjob, screwball, headcase. madman, rum, madwoman. cranky, unnatural, maniac. lunatic, unreal.

Usage examples for eccentric

  1. " He is more than eccentric Monsieur Dupont stated. – The Crooked House by Brandon Fleming
  2. The heir had lived abroad, and had lived in such an exceedingly eccentric manner as to give ground for a suit de lunatico inquirendo, brought by another heir. – A Tale of a Lonely Parish by F. Marion Crawford
  3. We are always on the lookout for the odd, the eccentric the whimsical. – The Complete Essays of C. D. Warner by Charles Dudley Warner