Phraseology as a Subsystem of language

In linguistics, phraseology is the study of set or fixed expressions, such as idioms, phrasal verbs, and other types of multi-word lexical units, in which the component parts of the expression take on a meaning more specific than or otherwise not predictable from the sum of their meanings when used independently.

Distinctive features of phraseological units:
1. Integrity (or transference) of meaning;
2. Stability (lexical and grammatical)
3. Separability
4. Expressivity and emotiveness

Phraseological units
On the whole phraseological units, even if they present a certain pattern, do not generate new phrases. They are unique. word-group is the largest two-facet lexical unit comprising more than one word but expressing one global concept.

Set phrases
A set phrase or fixed phrase is a phrase whose parts are fixed, even if the phrase could be changed without harming the literal meaning.

Idioms
Idioms are fixed expressions that are usually not clear or obvious. The expression to feel under the weather, which means to feel unwell is a typical idiom. The words do not tell us what it means, but the context usually helps.

Two groups of idioms:
nominal
verbal

Classification of idioms
Grammaticalverb + objecthold someone's hand [to take care of]
By meaningverb + preposition phraserise the eyebrows [to wonder]
By verb or another key wordHis fingers are all thumbs [clumsy].Do you mind my smoking? [object to]