The Collaborative International Dictionary of English v.0.48:

Forelock \Fore"lock`\, n.
   1. The lock of hair that grows from the forepart of the head.
      [1913 Webster]

   2. (Mech.) A cotter or split pin, as in a slot in a bolt, to
      prevent retraction; a linchpin; a pin fastening the
      cap-square of a gun.
      [1913 Webster]

   Forelock bolt, a bolt retained by a key, gib, or cotter
      passing through a slot.

   Forelock hook (Rope Making), a winch or whirl by which a
      bunch of three yarns is twisted into a standard. --Knight.


   To take time by the forelock or To take occasion by the
   forelock, to make prompt use of anything; not to let slip an
      opportunity.
      [1913 Webster]

            Time is painted with a lock before and bald behind,
            signifying thereby that we must take time by the
            forelock; for when it is once past, there is no
            recalling it.                         --Swift.
      [1913 Webster]

            On occasion's forelock watchful wait. --Milton.
      [1913 Webster]