The article contains a definition and a characterization of such an important quality of linguistic units as their semantic integrity (indivisibility of meaning). Arguments are offered in favour of the view that semantic integrity is characteristic not only of idioms (language units) but also of certain free word groups (speech units). The author reveals similarity and difference between stable and unstable semantically integral word groups, demonstrates the specificity of partial and full semantic integrity of linguistic units, ascertains the substantial features of idioms that constitute its definition. Word groups are divided into four classes by two pairs of distinctive features: ‘± language stability’ and ‘± semantic integrity’. Idioms as a peculiar class of word groups are opposed to the three other classes by different sets of features. A conclusion is drawn that semantically integral free word groups are not idioms, but they are similar to idioms by three substantial features and are one of the sources of the idiom fund replenishment.
semantic integrity, semantic divisibility, language stability, idiom, free word group.