In its narrowest sense, a synonym is a word or phrase that is perfectly substitutable in a context for another word or phrase. People who study language professionally agree that there is no such thing as an ideal synonym, for it is virtually impossible to find two words or phrases that are identical in denotation (meaning), connotation, frequency, familiarity, and appropriateness. Indeed, linguists have long noted the economy of language, which suggests that no language permits a perfect fit, in all respects, between any two words or phrases.