The Collaborative International Dictionary of English v.0.48:

Somehow \Some"how`\ (s[u^]m"hou`), adv.
   In one way or another; in some way not yet known or
   designated; by some means; as, the thing must be done
   somehow; he lives somehow.
   [1913 Webster]

         By their action upon one another they may be swelled
         somehow, so as to shorten the length.    --Cheyne.
   [1913 Webster]

   Note: The indefiniteness of somehow is emphasized by the
         addition of or other.
         [1913 Webster]

               Although youngest of the familly, he has somehow
               or other got the entire management of all the
               others.                            --Sir W.
                                                  Scott.
         [1913 Webster] Somersault

WordNet (r) 3.0 (2006):

somehow
    adv 1: in some unspecified way or manner; or by some unspecified
           means; "they managed somehow"; "he expected somehow to
           discover a woman who would love him"; "he tried to make
           is someway acceptable" [syn: somehow, someway,
           someways, in some way, in some manner]
    2: for some unspecified reason; "It doesn't seem fair somehow";
       "he had me dead to rights but somehow I got away with it";

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "somehow":
   accidentally, after a fashion, anyhow, anyway, anywise,
   as it chanced, by a fluke, by accident, by chance, by good fortune,
   by hazard, by some means, casually, for some reason, fortuitously,
   in, in some way, incidentally, no matter how, perchance,
   somehow or other, someway, unpredictably