means Slender pointed pieces of metal used to fasten, secure, or hold things in place — and, in slang, the legs you stand on.

from From Old English 'pinn,' meaning a peg or bolt, likely borrowed from Latin 'pinna' (a feather, point, or pinnacle). The sense traveled from wooden pegs to the fine metal fasteners we know today as the craft of pin-making sharpened over the centuries. The slang 'pins' for legs is a much later, jauntier offshoot — thin and supporting, like the things themselves.