The Collaborative International Dictionary of English v.0.48:

Sophomore \Soph"o*more\, n. [Probably fr. soph or sophister +
   Gr. ? foolish. The word was probably introduced into the
   United States at an early date, from the University of
   Cambridge, England. Among the cant terms at that university,
   as given in the Gradus ad Cantabrigiam, we find Soph-Mor as
   "the next distinctive appellation to Freshman," but the term
   has now almost ceased to be known at the English university
   from whence it came.]
   One belonging to the second of the four classes in an
   American college, or one next above a freshman. [Formerly
   written also sophimore.]
   [1913 Webster] Sophomoric

WordNet (r) 3.0 (2006):

sophomore
    adj 1: used of the second year in United States high school or
           college; "the sophomore class"; "his sophomore year"
           [syn: sophomore(a), second-year]
    n 1: a second-year undergraduate [syn: sophomore, soph]