Source : Webster's Revised Unabridged Dictionary (1913)

Lesser \Less"er\, adv.
   Less. [Obs.] --Shak.

Lesser \Less"er\ (-[~e]r), a. [This word is formed by adding
   anew the compar. suffix -er (in which r is from an original
   s) to less. See {Less}, a.]
   Less; smaller; inferior.

         God made . . . the lesser light to rule the night.
                                                  --Gen. i. 15.

   Note: Lesser is used for less, now the compar. of little, in
         certain special instances in which its employment has
         become established by custom; as, Lesser Asia (i. e.,
         Asia Minor), the lesser light, and some others; also in
         poetry, for the sake of the meter, and in prose where
         its use renders the passage more euphonious.

               The more my prayer, the lesser is my grace.
                                                  --Shak.

               The larger here, and there the lesser lambs.
                                                  --Pope.

               By the same reason may a man, in the state of
               nature, punish the lesser breaches of the law.
                                                  --Locke.

Source : WordNet®

lesser
     adj 1: of less size or importance; "the lesser anteater"; "the
            lesser of two evils" [ant: {greater}]
     2: smaller in size or amount or value; "the lesser powers of
        Europe"; "the lesser anteater"