IPA: //ʌnˈsoʊn//
KK: /ʌnˈsoʊn/
Not stitched or fastened together with thread.
The fabric was left unsewn, making it easy to alter later.
Unsewn → It is formed from "un-" (meaning not) and "sewn" (the past participle of "sew", which comes from Old English "siwian", meaning to stitch or join together). The word "unsewn" means not stitched or joined together.
Think of 'not' ('un-') being applied to something that has been 'stitched' ('sewn') — that's why unsewn means it hasn't been stitched.