Collocational restriction is a linguistic term used in morphology

Morphology (linguistics)

In linguistics, morphology is the identification, analysis and description, in a language, of the structure of morphemes and other linguistic units, such as words, affixes, parts of speech, intonation/stress, or implied context...

. The term refers to the fact that in certain two-word phrases the meaning of an individual word

Word

In language, a word is the smallest free form that may be uttered in isolation with semantic or pragmatic content . This contrasts with a morpheme, which is the smallest unit of meaning but will not necessarily stand on its own...

 is restricted to that particular phrase

Phrase

In everyday speech, a phrase may refer to any group of words. In linguistics, a phrase is a group of words which form a constituent and so function as a single unit in the syntax of a sentence. A phrase is lower on the grammatical hierarchy than a clause....

 (cf. idiom

Idiom

Idiom is an expression, word, or phrase that has a figurative meaning that is comprehended in regard to a common use of that expression that is separate from the literal meaning or definition of the words of which it is made...

). For instance: the adjective

Adjective

In grammar, an adjective is a 'describing' word; the main syntactic role of which is to qualify a noun or noun phrase, giving more information about the object signified....

 dry can only mean 'not sweet' in combination with the noun

Noun

In linguistics, a noun is a member of a large, open lexical category whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition .Lexical categories are defined in terms of how their members combine with other kinds of...

wine.

A more illustrative example is the one given below:

• white wine
• white coffee
• white noise
• white man

All four instances of white can be said to be idiomatic because in combination with certain nouns the meaning of white changes. In none of the examples does white have its usual meaning. Instead, in the examples above it means 'yellowish', 'brownish', 'containing many frequencies with about equal amplitude', and 'pinkish' or 'pale brown', respectively.