The Collaborative International Dictionary of English v.0.48:

D'ebut \D['e]`but"\, n. [F. d['e]but, prop., the first cast or
   throw at play, fr. but aim, mark. See Butt an end.]
   A beginning or first attempt; hence, a first appearance
   before the public, as of an actor or public speaker. Debutant

WordNet (r) 3.0 (2006):

debut
    n 1: the act of beginning something new; "they looked forward to
         the debut of their new product line" [syn: introduction,
         debut, first appearance, launching, unveiling,
         entry]
    2: the presentation of a debutante in society
    v 1: present for the first time to the public; "The band debuts
         a new song or two each month"
    2: appear for the first time in public; "The new ballet that
       debuts next months at Covent Garden, is already sold out"
    3: make one's debut; "This young soprano debuts next month at
       the Metropolitan Opera"

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "debut":
   appear, benefit, bill, come out, coming out, coming-out party,
   curtain raiser, embarkation, embarkment, enter, entertainment,
   exhibit, exhibition, farewell performance, first appearance,
   flesh show, floating, flotation, inaugural address, inauguration,
   induction, initiation, installation, installment, introduction,
   launch, launching, maiden speech, opener, performance, preliminary,
   premiere, presentation, presentment, production, show,
   stage presentation, swan song, theatrical performance, tryout,
   unveiling