Colloquialism(n.) An expression used in informal conversation, not employed in formal discourse or writing.
Thesaurus Entries
Gothicism, Irish bull, Neanderthalism, age of ignorance, animality, antiphrasis, bad taste, barbarity, barbarousness, benightedness, benightment, bestiality, bombasticness, brutality, brutishness, cacology, cacophony, clumsiness, coarseness, colloquialism, corruption, crudeness, cumbrousness, dark, dark age, darkness, dysphemism, error, foreignism, gracelessness, grossness, harshness, heathenism, heaviness, ill breeding, ill-balanced sentences, impoliteness, impropriety, impurity, incivility, inconcinnity, incorrectness, indecorousness, inelegance, inelegancy, infelicity, lack of finish, lack of polish, lapse, leadenness, localism, malaprop, malapropism, misconstruction, missaying, misusage, misuse, neologism, paganism, philistinism, pompousness, ponderousness, poor diction, roughness, rudeness, savagery, savagism, sesquipedalianism, sesquipedality, shibboleth, slang, slip, slipshod construction, solecism, spoonerism, stiltedness, taboo word, tastelessness, troglodytism, turgidity, uncivilizedness, uncouthness, uncultivatedness, uncultivation, unculturedness, unenlightenment, uneuphoniousness, ungracefulness, ungrammaticism, unrefinement, unseemliness, unwieldiness, vernacularism, vulgarism, vulgarity, wildness