Webster says :
pin (pin) n., v. <pinned, pin-ning>
n.
1. a small, slender, often pointed piece of
metal, wood, etc., used as a fastener or
support.
2. a short, slender piece of wire with a
point at one end and a head at the
other, for fastening things together.
3. any of various forms of fasteners,
badges, or ornaments consisting
essentially or partly of a penetrating
wire or shaft (often used in
combination): a fraternity pin; a tiepin.
4. a. a short metal rod, as a linchpin,
driven through holes in adjacent
parts, as a hub and an axle, to
keep the parts together.
b. a short cylindrical rod or tube, as
a wrist pin or crankpin, joining
two parts so as to permit them to
move in one plane relative to each
other.