Lexical item different from lexical unit
In lexicography, a lexical item is a single word, a part of a word,  or a chain of words (catena) that forms the basic elements of a language's lexicon (≈ vocabulary). Examples are cat, traffic light, take care of, by the way, and it's raining cats and dogs. Lexical items can be generally understood to convey a single meaning, much as a lexeme, but are not limited to single words. Lexical items are like semes in that they are "natural units" translating between languages, or in learning a new language. In this last sense, it is sometimes said that language consists of grammaticalized lexis, and not lexicalized grammar. The entire store of lexical items in a language is called its lexis.
Lexical items composed of more than one word are also sometimes called  lexical chunks, gambits, lexical phrases, lexicalized stems, or speech formulae. The term polyword listemes is also sometimes used.