turncoat

This term carries a heavy negative charge, implying a profound breach of trust and a lack of integrity. It suggests not just a change of opinion, but a calculated betrayal of a former group for personal gain or survival, evoking an image of someone literally turning their coat to hide their original colors. As a countable noun, it follows standard English pluralization rules. It is typically used in political, military, or ideological contexts where loyalty is a primary value.