Stitch: (noun) one of the small lines of thread that you can see on a piece of fabric after it has been sewn/ (verb) to sew something, that is to say, to use a needle and thread to mend, join or decorate pieces of fabric.
in stitches– it is an informal expression that means to laugh a lot. ex. The play had us in stitches or The play was great! We all were in stitches.