The Collaborative International Dictionary of English v.0.48:

Freshman \Fresh"man\, n.; pl. Freshmen.
   A novice; one in the rudiments of knowledge; especially, a
   student during his first year in a high school, college, or
   university.

   Syn: frosh.
        [1913 Webster]

              He drank his glass and cracked his joke,
              And freshmen wondered as he spoke.  --Goldsmith.
        [1913 Webster]

   Freshman class, the lowest of the four classes in an
      American college. [ U. S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

freshman
    adj 1: used of a person in the first year of an experience
           (especially in United States high school or college); "a
           freshman senator"; "freshman year in high school or
           college" [syn: freshman, first-year]
    n 1: a first-year undergraduate [syn: freshman, fresher]
    2: any new participant in some activity [syn: newcomer,
       fledgling, fledgeling, starter, neophyte, freshman,
       newbie, entrant]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "freshman":
   abecedarian, alphabetarian, apprentice, articled clerk, baby,
   beginner, boot, cadet, catechumen, colt, deb, debutant, entrant,
   fledgling, greenhorn, greeny, ignoramus, inductee, infant,
   initiate, junior, learner, midshipman, neophyte, nestling, new boy,
   newcomer, novice, novitiate, plebe, postulant, probationer,
   probationist, raw recruit, recruit, rookie, senior, soph,
   sophomore, tenderfoot, trainee, tyro, undergrad, undergraduate,
   upperclassman