This is the 10269th most frequent Russian word.
больничный
"Больничный" refers to a sick leave or a medical certificate for sick leave.
Here, 'больничный' refers to 'sick leave', a time period granted to a worker for illness recovery.
Я взял больничный, чтобы отдохнуть и поправиться.
I took sick leave to rest and recover.
'Больничный' again means 'sick leave', specifically referring to the duration of it in this sentence.
Его больничный закончится в пятницу.
His sick leave will end on Friday.
In this use, 'больничный' relates to the documentation or note provided as proof of the sick leave.