A word-group is the largest two-facet lexical unit comprising more than one word but expressing one global concept.
The lexical meaning of the word groups is the combined lexical meaning of the component words. The meaning of the word groups is motivated by the meanings of the component members and is supported by the structural pattern. But it’s not a mere sum total of all these meanings! Polysemantic words are used in word groups only in 1 of their meanings. These meanings of the component words in such word groups are mutually interdependent and inseparable (blind man – «a human being unable to see», blind type – «the copy isn’t readable).
Word groups possess not only the lexical meaning, but also the meaning conveyed mainly by the pattern of arrangement of their constituents. The structural pattern of word groups is the carrier of a certain semantic component not necessarily dependent on the actual lexical meaning of its members (school grammar – «grammar which is taught in school», grammar school – «a type of school»). We have to distinguish between the structural meaning of a given type of word groups as such and the lexical meaning of its constituents.
Phraseological units are (according to Prof. Kunin A.V.) stable word-groups with partially or fully transferred meanings ("to kick the bucket", “Greek gift”, “drink till all's blue”, “drunk as a fiddler (drunk as a lord, as a boiled owl)”, “as mad as a hatter (as a march hare)”).
3 types of lexical combinability of words:
1). Free combination
Grammatical properties of words are the main factor of their combinability.
Ex.: I’m talking to you. You are writing.
Free combinations permit substitution of any of its elements without semantic change of the other element.
Ex.: to commit a murder
(Bread & butter, Dark night, Blue sky, Bright day)
They are the habitual associations of a word in a language with other particular words. Speakers become accustomed to such collocations.
Very often they are related to the referential & situational meaning of words.
Sometimes there are collocations, which are removed from the reference to extra-linguistic reality.
(collocations involving, colour words)
Ex.: to be green with jealousy
Idioms are also collocations, because they consist of several words that tend to be used together, but the difference – we can’t guess the meaning of the whole idiom from the meanings of its parts.
This criterion is called the degree of semantic isolation.
In different types of idioms – it is different.
Ex.: to cry a blue murder = to complain loudly