What is a Colloquialism?
Colloquialisms are expressions appropriate to informal spoken language but ordinarily inappropriate to more formal (usually written) language. Colloquialisms (from Latin colloqui, to speak with, converse) abound in spoken or familiar English and do not reflect unfavorably on the speaker's education. In this respect they are distinguished from slang, which is less widely acceptable and usually more ephemeral, and from cant, which is ordinarily unacceptable as well as obscure. See slang.
The distinction between colloquial language and dialect is one not of degree but of kind: colloquial language is standard for a broad level of usage, whereas dialectal language is standard only for a geographical region. In English, all usages were once dialectal; ultimately one dialect, the Midland, was promoted at the expense of the other dialects and became Standard English. See dialect.
Colloquialisms are often promoted to the rank of Standard English. This process is especially likely if the colloquial expression has no true equivalent in Standard English, if its equivalent is somehow inferior, or if the colloquialism exists only as a slightly different sense of an accepted word. Similarly, slang or dialect expressions may become colloquial. Any of these processes may be reversed.
Colloquialisms may be single words, such as "folks" for "relatives" ("Did you meet my folks?") or "tremendous" for "excellent" ("The movie was tremendous"); clipped words, such as "lab," "ad," or "bike"; short picturesque words for technical terms, such as "bugs" for "insects" or for "mechanical faults"; contractions, such as "we'll" or "can't"; and verb-adverb combinations, such as "put out" for "expel," "extinguish," "publish," "inconvenience," "embarrass," or "retire" (in baseball). Colloquial usage may also differ from Standard English in grammar, pronunciation, or connotation.