preposterous (adj.)

• absurd
• asinine
• balmy
• barmy
• baroque
• barred
• batty
• bizarre
• cockamamie
• crazy
• cutthroat
• dotty
• doubtable
• doubtful
• dubious
• dubitable
• exacting
• excessive
• exorbitant
• extortionate
• extraordinary
• extravagant
• extreme
• fanciful
• fancy
• fantastic
• fatuous
• florid
• foolish
• grotesque
• harebrained
• high-flown
• hopeless
• idiotic
• imbecilic
• immoderate
• implausible
• impossible
• inconceivable
• incredible
• inflationary
• inordinate
• insane
• irrational
• laughable
• loony
• ludicrous
• mad
• maggoty
• mindless
• monstrous
• moronic
• nonsensical
• notional
• nutty
• outlandish
• outrageous
• outre
• overpriced
• paradoxical
• potty
• problematic
• prohibited
• prohibitive
• questionable
• ridiculous
• risible
• rococo
• screwy
• self-contradictory
• senseless
• silly
• spiraling
• suspect
• suspicious
• tall
• thick
• thin
• unbelievable
• unconscionable
• unconvincing
• undeserved
• undeserving
• undue
• unearned
• unearthly
• unentitled
• ungodly
• unimaginable
• unjustified
• unmerited
• unreasonable
• unthinkable
• unwarranted
• unworthy
• usurious
• wacky
• weird
• whimsical
• wild