Synonyms for Illogical:

adj.

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

n.

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

Other synonyms:

sophistic, Unreasoned. specious. spurious. causeless
groundless.
indefensible
untenable.
unsystematic
unscientific.
Other relevant words:
baseless, casuistic, childish, confused, disconnected, disjointed, disordered, fallible, garbled, groundless, hollow, incoherent, inconclusive, inconsequent, inconsequential, intuitive, irrelevant, irresponsible, nonrational, nutty, perverse, scattered, screwy, sophistic, sophistical, specious, spurious, unconnected, unfounded, unlogical, unproved, unscientific, unsound, unsubstantial, untenable, visceral, wacky, wrong, Unreasoned, not following, without basis.

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
  3. Yet such negative implications are often repudiated as illogical – Logic, Inductive and Deductive by William Minto