The Collaborative International Dictionary of English v.0.48:

Lesser \Less"er\, adv.
   Less. [Obs.] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lesser \Less"er\ (l[e^]s"[~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.
   [1913 Webster]

         God made . . . the lesser light to rule the night.
                                                  --Gen. i. 15.
   [1913 Webster]

   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.
         [1913 Webster]

               The more my prayer, the lesser is my grace.
                                                  --Shak.
         [1913 Webster]

               The larger here, and there the lesser lambs.
                                                  --Pope.
         [1913 Webster]

               By the same reason may a man, in the state of
               nature, punish the lesser breaches of the law.
                                                  --Locke.
         [1913 Webster]

WordNet (r) 3.0 (2006):

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"

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "lesser":
   abated, ablated, attenuated, bated, belittled, common, consumed,
   contracted, curtailed, decreased, deflated, demeaning, diminished,
   dinky, disadvantaged, dissipated, dropped, eroded, fallen, humble,
   in the shade, inferior, infra dig, insignificant, junior, less,
   low, lower, lowered, lowly, miniaturized, minor, modest, nether,
   ordinary, reduced, retrenched, scaled-down, second rank,
   second string, secondary, servile, shorn, shorter, shrunk,
   shrunken, small, small-fry, small-time, smaller, sub, subaltern,
   subjacent, subject, subordinate, subservient, third rank,
   third string, under, underprivileged, vulgar, watered-down,
   weakened, worn