string of words vs word string

string of words and word string both are nouns.

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

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

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

Other synonyms of string of words include linguistic string.

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