plain stitch vs knitting stitch

plain stitch and knitting stitch both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain stitch	Yes	No	No	No
knitting stitch	Yes	No	No	No

As nouns, knitting stitch is a hypernym of plain stitch; that is, knitting stitch is a word with a broader meaning than plain stitch:

plain stitch: a basic knitting stitch made by putting the needle through the front of the stitch from the lefthand side
knitting stitch: a stitch taken in knitting

plain stitch (noun)	knitting stitch (noun)
a basic knitting stitch made by putting the needle through the front of the stitch from the lefthand side	a stitch taken in knitting