gums (of the teeth), to dispute
齗 centers on the gums as the fleshy tissue surrounding the teeth. The meaning 'to dispute' is a separate, likely extended sense related to baring the gums in argument, but the primary concrete meaning is gums.
齗 combines 齒 (tooth) with 斤, which likely provides the sound. The original meaning is gums, with 'dispute' possibly arising from a metaphorical extension.
The left side 齒 shows teeth, and the right side 斤 looks like an axe. Imagine the gums as the tough tissue that holds the teeth in place, like an axe handle holds the blade.
For キン, picture a king (キン) with a toothy grin, his gums showing as he disputes a claim. King -> キン.