WordNet sense 1 (any new participant in some activity):

entrant, neophyte, newbie, newcomer, starter, fledgeling, fledgling

WordNet sense 2 (a first-year undergraduate):

fresher

WordNet sense 3 (used of a person in the first year of an experience (especially in United States high school or college)):

first-year

WordNet sense 4 (preceding all others in time or space or degree):

first