Subtle acknowledgment

NOD

A slight tilt of the head often means "yes" or "I understand."

A "subtle acknowledgment" hints at a small, wordless gesture people use to show they’ve noticed or agreed with something. The answer "NOD" fits perfectly because it’s a simple tilt of the head often used as a quiet response. There’s no wordplay here—just a straightforward definition matching a common action. Think of nodding in a meeting or across a room to signal understanding without speaking.