Synonyms and related words :
astonishment, bellyacher, blockbuster, blow, bomb, bombshell, boundary condition, catch, clause, complainant, complainer, condition, crab, crank, croaker, donnee, earthshaker, escalator clause, escape clause, escape hatch, eye-opener, faultfinder, fine print, frondeur, given, griper, grouch, grounds, grouser, growler, grumbler, joker, kvetch, limiting condition, malcontent, murmurer, mutterer, obligation, parameter, peripeteia, prerequisite, provision, provisions, proviso, querulous person, reactionary, reactionist, rebel, requisite, revelation, saving clause, shocker, sine qua non, small print, sorehead, sourpuss, specification, staggerer, startler, stipulation, string, surprisal, surprise, surprise ending, surprise package, surprise party, switch, terms, thunderbolt, thunderclap, ultimatum, whereas, whiner