This is the 14113th most frequent Polish word.
pozszywać
To sew together.
In this usage, 'pozszywać' refers to mending clothes, implying repairing them by sewing.
Muszę pozszywać ubrania przed wyjazdem.
I have to mend the clothes before the trip.
Here, 'pozszywać' describes the preliminary stitching of fabric as a preparatory step for creating something new, like the costume mentioned.
Pozszywawszy materiał, uszyła nowy kostium.
Having stitched the fabric, she sewed a new costume.
Here, 'pozszywać' means to stitch together, signifying the action of sewing something together, which in this context refers to the pages of the book.