word string vs string of words

word string and string of words both are nouns.

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

As nouns, word string and string of words are synonyms defined as:

word string and string of words: a linear sequence of words as spoken or written

Other synonyms of word string include linguistic string.

word string (noun)	string of words (noun)
a linear sequence of words as spoken or written	a linear sequence of words as spoken or written