Source : Webster's Revised Unabridged Dictionary (1913)

Lamb \Lamb\ (l[a^]m), n. [AS. lamb; akin to D. & Dan. lam, G. &
   Sw. lamm, OS., Goth., & Icel. lamb.]
   1. (Zo["o]l.) The young of the sheep.

   2. Any person who is as innocent or gentle as a lamb.

   3. A simple, unsophisticated person; in the cant of the Stock
      Exchange, one who ignorantly speculates and is victimized.

   {Lamb of God}, {The Lamb} (Script.), the Jesus Christ, in
      allusion to the paschal lamb.

            The twelve apostles of the Lamb.      --Rev. xxi.
                                                  14.

            Behold the Lamb of God, which taketh away the sin of
            the world.                            --John i. 29.

   {Lamb's lettuce} (Bot.), an annual plant with small obovate
      leaves ({Valerianella olitoria}), often used as a salad;
      corn salad. [Written also {lamb lettuce}.]

   {Lamb's tongue}, a carpenter's plane with a deep narrow bit,
      for making curved grooves. --Knight.

   {Lamb's wool}.
      (a) The wool of a lamb.
      (b) Ale mixed with the pulp of roasted apples; -- probably
          from the resemblance of the pulp of roasted apples to
          lamb's wool. [Obs.] --Goldsmith.

Lettuce \Let"tuce\ (l[e^]t"t[i^]s), n. [OE. letuce, prob.
   through Old French from some Late Latin derivative of L.
   lactuca lettuce, which, according to Varro, is fr. lac,
   lactis, milk, on account of the milky white juice which flows
   from it when it is cut: cf. F. laitue. Cf. {Lacteal},
   {Lactucic}.] (Bot.)
   A composite plant of the genus {Lactuca} ({L. sativa}), the
   leaves of which are used as salad. Plants of this genus yield
   a milky juice, from which lactucarium is obtained. The
   commonest wild lettuce of the United States is {L.
   Canadensis}.

   {Hare's lettuce}, {Lamb's lettuce}. See under {Hare}, and
      {Lamb}.

   {Lettuce opium}. See {Lactucarium}.

   {Sea lettuce}, certain papery green seaweeds of the genus
      {Ulva}.

Source : WordNet®

lamb's lettuce
     n : widely cultivated as a salad crop and pot herb; often a weed
         [syn: {common corn salad}, {Valerianella olitoria}, {Valerianella
         locusta}]