Synonyms for Illogical:

adj.

absurd (adjective)
crazy, farcical, foolish, eccentric, fallacious, irrational, preposterous, contradictory, invalid, anachronistic, ridiculous, self-contradictory, paradoxical, idiotic, inane, nonsensical, ludicrous, screwy, meaningless, implausible, bizarre, silly, absurd, incongruous, impossible, outlandish, senseless, inconsistent.
all (adjective)
unlogical.
disconnected (adjective)
garbled, disjointed, incoherent, disordered.
erroneous (adjective)
distorted, flawed, inaccurate, miscalculated, erroneous, botched, false, fallacious, mistaken, Misconstrued, incorrect, misjudged, misestimated, defective, marred, Misconceived, faulty.
fallacious (adjective)
unfounded, erroneous, Unreasoned, mistaken.
false (adjective)
unsound.
far-fetched (adjective)
eccentric, bizarre, inconsequential, doubtful.
flimsy (adjective)
baseless.
illogical (adjective)
faulty, screwy, irrational, irrelevant, inconsistent, inconsequent, preposterous, implausible, incongruous, untenable, without basis, hollow, specious, casuistic, sophistic, not following, unproved, inconclusive, false, unsound, wacky, unscientific, without foundation, sophistical, fallacious, incorrect, nutty, self-contradictory, meaningless, absurd, groundless, senseless, spurious, fatuous, unsubstantial, unconnected, invalid, unreasonable.
impractical/impracticable (adjective)
speculative, impossible.
inane (adjective)
vacant, mindless, vacuous, ridiculous.
incongruous (adjective)
distorted, contradictory.
indefensible (adjective)
untenable.
senseless (adjective)
without rhyme or reason.
thoughtless (adjective)
empty-headed, mindless, vacuous, unthinking, vacant, unoccupied, blank, unthoughtful, fatuous, thoughtless, brainless, inane, unreasonable.
unfounded (adjective)
without foundation, without basis.

n.

perverse, irresponsible, extreme, hysterical, childish. Unreasoned, reason. illogical (noun)
disconnected, absurd, confused, disordered, incoherent, intuitive, unconnected, nonrational, garbled, visceral, unlogical, inconsequential, unreasonable, scattered, disjointed.
irrational (noun)
unscientific, inconsequent, having the cart before the horse, out of bounds, unsound, screwy, groundless, wrong, wacky, nutty, without basis, inconclusive, without rhyme or reason, biased, unproved, paralogistic, baseless, jesuitical, hollow, fallible, sophistical, far-out, irrelevant, specious, kafkaesque, not following, not ringing true, prejudiced, untenable, casuistic, dopey, without foundation, unsubstantial.

Other synonyms:

Unreasoned, sophistic. specious. spurious. causeless
groundless.
indefensible
untenable.
unsystematic
unscientific.

Usage examples for illogical

  1. And he must be satisfied with what he sees or our illogical actions wouldn't worry him so little." – Mystery Ranch by Arthur Chapman
  2. Yet into this entirely illogical position the Commonwealth was steadily drifting. – The Life of John of Barneveld, 1609-15, Volume I. by John Lothrop Motley Last Updated: February 7, 2009