WordNet (r) 3.0 (2006):

shutdown
    n 1: termination of operations; "they regretted the closure of
         the day care center" [syn: closure, closedown,
         closing, shutdown]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "shutdown":
   abandonment, blockade, breakoff, cease, ceasing, cessation, close,
   closing, closure, desinence, desistance, discontinuance,
   discontinuation, occlusion, relinquishment, renunciation, shutting,
   shutting up, stopping, surcease, termination