Knife-edge and Lapel

Knife-edge noun - A narrow boundary.

Lapel and knife-edge are semantically related in fold topic. In some cases you can use "Lapel" instead a noun phrase "Knife-edge", when it comes to topics like double thickness.

Lapel noun - Lap at the front of a coat; continuation of the coat collar.

Knife-edge and lapel are semantically related in fold topic. You can use "Knife-edge" instead a noun "Lapel", if it concerns topics such as double thickness.