c.1470, "not endowed with reason" (of beats, etc.), from L. irrationalis "without reason," from in- "not" + rationalis "reason" (see reason). Meaning "illogical, absurd" is attested from 1641.
Ab*surd"\, a. [L. absurdus harsh-sounding; ab + (prob) a derivative fr. a root svar to sound; not connected with surd: cf. F. absurde. See Syringe.] Contrary to reason or propriety; obviously and fiatly opposed to manifest truth; inconsistent with the plain dictates of common sense; logically contradictory; nonsensical; ridiculous; as, an absurd person, an absurd opinion; an absurd dream. This proffer is absurd and reasonless. --Shak. 'This phrase absurd to call a villain great. --Pope. --p. 9 Syn: Foolish; irrational; ridiculous; preposterous; inconsistent; incongruous. Usage: Absurd, Irrational, Foolish, Preposterous. Of these terms, irrational is the weakest, denoting that which is plainly inconsistent with the dictates of sound reason; as, an irrational course of life. Foolish rises higher, and implies either a perversion of that faculty, or an absolute weakness or fatuity of mind; as, foolish enterprises. Absurd rises still higher, denoting that which is plainly opposed to received notions of propriety and truth; as, an absurd man, project, opinion, story, argument, etc. Preposterous rises still higher, and supposes an absolute inversion in the order of things; or, in plain terms, a "putting of the cart before the horse;" as, a preposterous suggestion, preposterous conduct, a preposterous regulation or law.
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