gusset, gore
襠 centers on a reinforcing or expanding piece of fabric: a gusset inserted into a garment for shape or strength, or a gore adding width. Both meanings share the idea of a shaped cloth panel sewn into a larger piece.
襠 combines 衤 (clothing) with 當, which likely contributes the sound トウ. The character originally referred to the crotch piece or gusset in traditional clothing, and by extension a gore or panel in garments.
The clothing radical 衤 beside 當 suggests a piece of cloth added to a garment. Picture a tailor sewing a triangular gusset into a kimono to give it more room.
For トウ, imagine a tailor sewing a gusset into a toe of a giant sock: toe -> トウ, and the cloth panel reinforces the toe area.