Definitions for sick leave
Random House Webster's College Dictionary
leave from duty, work, or the like, granted because of illness.
Origin of sick leave:
a leave of absence from work because of illness
Kernerman English Learner's Dictionary
sick leave(noun)ˈsɪk ə nɪŋ
paid time off from work if you are ill
How much sick leave am I entitled to?
Paid absence from work specifically to recover from illness.
U.S. National Library of Medicine
An absence from work permitted because of illness or the number of days per year for which an employer agrees to pay employees who are sick. (Webster's New Collegiate Dictionary, 1981)