Modifier is a functional label for an element in a phrase which supports (or 'modifies') the Head word.
One word or phrase modifies another by making its meaning more specific.
Because the two words make a phrase, the ‘modifier’ is normally close to the modified word.
In the phrase primary-school teacher:
- teacher is modified by primary-school (to mean a specific kind of teacher)
- school is modified by primary (to mean a specific kind of school).
Other examples of modifiers are happy in the noun phrase a happy bunny, very in the adjective phrase very cheeky and extremely in the adverb phrase extremely quickly.