col·lo·qui·al·ism \-ˌlizəm\noun (-s) 1. a.: an expression considered more appropriate to familiar conversation than to formal speech or to formal writing < slang words frequently rise to the rank of colloquialisms — G.L.Kittredge > b.: an expression belonging to local or regional dialect — not used technically 2.: informal or conversational style in language < the appeal of Wordsworth's colloquialism >