stitch vs sew together

stitch is a noun but sew together is not a noun.

Word	Noun	Adjective	Verb	Adverb
stitch	Yes	No	Yes	No
sew together	No	No	Yes	No

As verbs, stitch and sew together are synonyms defined as:

Other synonyms of stitch include run up, sew.

stitch (noun)	sew together (noun)
a link or loop or knot made by an implement in knitting, crocheting, embroidery, or sewing
a sharp spasm of pain in the side resulting from running

stitch (verb)	sew together (verb)
fasten by sewing; do needlework	fasten by sewing; do needlework