syntagm vs string of words

syntagm and string of words both are nouns.

Word	Noun	Adjective	Verb	Adverb
syntagm	Yes	No	No	No
string of words	Yes	No	No	No

As nouns, string of words is a hypernym of syntagm; that is, string of words is a word with a broader meaning than syntagm:

syntagm: a syntactic string of words that forms a part of some larger syntactic unit
string of words: a linear sequence of words as spoken or written

Other hypernyms of syntagm include linguistic string, word string.

syntagm (noun)	string of words (noun)
a syntactic string of words that forms a part of some larger syntactic unit	a linear sequence of words as spoken or written