ornamental trappings under collar
靳 refers to ornamental trappings worn under a horse's collar, a specific piece of decorative harness. Its meaning is narrow and concrete, centered on this particular equestrian accessory.
靳 combines 革 (leather) with 斤, which likely contributes the sound. The character is associated with leather horse trappings, fitting the leather radical.
Leather 革 and an axe-like shape 斤 suggest a crafted leather piece: imagine ornamental leather trappings fitted under a horse's collar, shaped and trimmed with a tool.
For キン, picture a king's horse wearing ornamental leather trappings: king -> キン, and the leather 革 piece is fit for royalty.