shoe lace vs shoe string

shoe lace and shoe string both are nouns.

Word	Noun	Adjective	Verb	Adverb
shoe lace	Yes	No	No	No
shoe string	Yes	No	No	No

As nouns, shoe lace and shoe string are synonyms defined as:

Other synonyms of shoe lace include shoelace, shoestring.

shoe lace (noun)	shoe string (noun)
a lace used for fastening shoes	a lace used for fastening shoes
	a small amount of money