:Lexical item:

(1) A word

(2) A word such as a noun, main verb, adjective, or adverb. In this sense lexical item is contrasted with grammatical item (pronoun, preposition, conjunction, auxiliary verb, modal verb). A frequent use of the term in this sense is in the specification of unmarked and marked tonicity. In English at least unmarked tonicity, apart from in a few exceptional grammatical structures, has the nucleus on the final lexical item in the intonation phrase.

Also called content word.
An alternative for grammatical item is function word.