means To beat or pulse with a strong, rhythmic intensity — as a wound, a heart, or an ache does when it makes itself felt.

from An echoic word, born from the sound and feel of the thing itself — that dull repeated pounding. It surfaces in Middle English as 'throbben,' and like 'throb,' 'thrum,' and 'thump,' it belongs to a small family of words that imitate a heavy, recurring beat rather than descending from any single ancient root.