WordNet sense 1 (the official who signals the beginning of a race or competition):

dispatcher

WordNet sense 2 (any new participant in some activity):

entrant, freshman, neophyte, newbie, newcomer, fledgeling, fledgling

WordNet sense 3 (food or drink to stimulate the appetite (usually served before a meal or as the first course)):

appetizer, appetiser

WordNet sense 4 (an electric motor for starting an engine):

starter motor, starting motor

WordNet sense 5 (a hand tool consisting of a rotating shaft with parallel handle):

crank