to seize, to clutch, to arrest, to capture
捦 centers on taking hold of something firmly and not letting go: seizing, clutching, arresting, or capturing.
捦 combines 扌 (hand) with 金, which likely contributes the sound. The exact historical development is uncertain, but the hand component clearly relates to seizing or holding.
A hand 扌 clutching a piece of gold 金 so tightly that no one can take it away: seizing and capturing it.
For キン, imagine a hand seizing a golden key: key -> キン, and the hand clutches it firmly.