Clamming up and Self-willed

Self-willed and clamming up are semantically related. In some cases you can use "Self-willed" instead an adjective "Clamming up".

Self-willed adjective - Sticking to an opinion, purpose, or course of action in spite of reason, arguments, or persuasion.

Clamming up and self-willed are semantically related. Sometimes you can use "Clamming up" instead an adjective phrase "Self-willed".