WordNet (r) 3.0 (2006):

deadline
    n 1: the point in time at which something must be completed

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "deadline":
   A-day, D day, H hour, border line, bound, boundary,
   boundary condition, boundary line, bourn, break boundary,
   breakoff point, ceiling, charged moment, circumscription, compass,
   confine, critical moment, crucial moment, cutoff, cutoff point,
   decisive moment, delimitation, determinant, division line,
   eleventh hour, end, extremity, finish, floor, frontier, hedge,
   high-water mark, interface, kairos, kairotic moment, limen, limit,
   limitation, limiting factor, line, line of demarcation,
   low-water mark, lower limit, march, mark, mete, moment of truth,
   nick of time, pregnant moment, psychological moment, start,
   starting line, starting point, target date, term, terminal date,
   terminus, threshold, time allotment, upper limit, zero hour