Difference in terminology (“set-phrases”, “idioms” and “word-equivalents” [1]) reflects certain differences in the main criteria used to distinguish types of phraseological units and free word-groups. The term “set phrase” implies that the basic criterion of differentiation is stability of the lexical components and grammatical structure of word-groups.
There is a certain divergence of opinion as to the essential features of phraseological units as distinguished from other word-groups and the nature of phrases that can be properly termed “phraseological units”. The habitual terms “set-phrases”, “idioms”, “word-equivalents” are sometimes treated differently by different linguists. However these terms reflect to certain extend the main debatable points of phraseology which centre in the divergent views concerning the nature and essential features of phraseological units as distinguished from the so-called free word-groups [2, p. 100].
The term “set expression” implies that the basic criterion of differentiation is stability of the lexical components and grammatical structure of word-groups.
The term “word-equivalent” stresses not only semantic but also functional inseparability of certain word-groups, their aptness to function in speech as single words.
The term “idioms” generally implies that the essential feature of the linguistic units under consideration is idiomaticity or lack of motivation. Uriel Weinreich expresses his view that an idiom is a complex phrase, the meaning of which cannot be derived from the meanings of its elements. He developed a more truthful supposition, claiming that an idiom is a subset of a phraseological unit. Ray Jackendoff and Charles Fillmore offered a fairly broad definition of the idiom, which, in Fillmore’s words, reads as follows: “…an idiomatic expression or construction is something a language user could fail to know while knowing everything else in the language”. Chafe also