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]

WordNet (r) 3.0 (2006):

lambda
    n 1: the 11th letter of the Greek alphabet
    2: the craniometric point at the junction of the sagittal and
       lamboid sutures of the skull

The Free On-line Dictionary of Computing (30 December 2018):

LAMBDA

   A version of typed lambda-calculus, used to describe
   semantic domains.

   ["Outline of a Mathematical Theory of Computation",
   D.S. Scott, TM PRG-2, PRG, Oxford U, 1971].