WordNet (r) 3.0 (2006):

sick leave
    n 1: a leave of absence from work because of illness

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "sick leave":
   AWOL, French leave, abscondence, absence, absence without leave,
   absentation, absenteeism, absenting, cut, day off, default,
   departure, disappearance, escape, excused absence, fleeing,
   furlough, holiday, hooky, leave, leave of absence, leaving,
   nonappearance, nonattendance, running away, sabbatical leave,
   truancy, truantism, unexcused absence, vacation