WordNet (r) 3.0 (2006):

day off
    n 1: a day when you are not required to work; "Thursday is his
         day off"

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "day off":
   AWOL, French leave, High Holiday, High Holy Day, abeyance,
   abscondence, absence, absence without leave, absentation,
   absenteeism, absenting, bank holiday, break, caesura, cease-fire,
   church feast, cut, day of festivities, default, departure,
   disappearance, drop, escape, excused absence, feast, feast day,
   festival day, fete day, fixed feast, fleeing, furlough, gala day,
   hesitation, high day, holiday, holy day, hooky, interim, interlude,
   intermezzo, intermission, intermittence, interruption, interval,
   lapse, layoff, leave, leave of absence, leaving, legal holiday,
   letup, lull, nonappearance, nonattendance, pause, recess,
   red-letter day, remission, respite, rest, running away,
   sabbatical leave, sick leave, stand-down, stay, suspension,
   truancy, truantism, truce, unexcused absence, vacation