The Collaborative International Dictionary of English v.0.48:

Lambda \Lamb"da\, n. [NL., fr. Gr. la`mbda.]
   1. The name of the Greek letter [Lambda], [lambda],
      corresponding with the English letter L, l.
      [1913 Webster]

   2. (Anat.) The point of junction of the sagittal and lambdoid
      sutures of the skull.
      [1913 Webster]

   3. (Phys.) A subatomic particle carrying no charge, having a
      mass equal to 2183 times that of an electron; it decays
      rapidly, typically forming a nucleon and a pion. --MW10
      [PJC]

   Lambda moth (Zool.), a moth so called from a mark on its
      wings, resembling the Greek letter lambda ([Lambda]).
      [1913 Webster]