The Collaborative International Dictionary of English v.0.48:

Leak \Leak\ (l[=e]k), n. [Akin to D. lek leaky, a leak, G. leck,
   Icel. lekr leaky, Dan. l[ae]k leaky, a leak, Sw. l[aum]ck;
   cf. AS. hlec full of cracks or leaky. Cf. Leak, v.]
   1. A crack, crevice, fissure, or hole which admits water or
      other fluid, or lets it escape; as, a leak in a roof; a
      leak in a boat; a leak in a gas pipe. "One leak will sink
      a ship." --Bunyan.
      [1913 Webster]

   2. The entrance or escape of a fluid through a crack,
      fissure, or other aperture; as, the leak gained on the
      ship's pumps.
      [1913 Webster]

   3. (Elec.) A loss of electricity through imperfect
      insulation; also, the point at which such loss occurs.
      [Webster 1913 Suppl.]

   4. an act of urinating; -- used mostly in the phrase

   take a leak, i. e. to urinate. [vulgar]
      [PJC]

   5. The disclosure of information that is expected to be kept
      confidential; as, leaks by the White House staff
      infuriated Nixon; leaks by the Special Prosecutor were
      criticized as illegal.
      [PJC]

   To spring a leak, to open or crack so as to let in water;
      to begin to let in water; as, the ship sprung a leak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

take a leak
    v 1: eliminate urine; "Again, the cat had made on the expensive
         rug" [syn: make, urinate, piddle, puddle,
         micturate, piss, pee, pee-pee, make water,
         relieve oneself, take a leak, spend a penny, wee,
         wee-wee, pass water]