Irreversible binomial

In grammar, irreversible binomial is a noun phrase. It consists of two nouns which are joined by a conjunction. It is to be noted, that the order of the nouns are conventionally fixed.

For example, the noun phrase bread and butter is an irreversible binomial which is joined by the conjunction 'and', and the conventional order of the nouns 'bread' and 'butter' cannot be changed.