Be sick in back yard regularly (5)
I believe the answer is:
daily
'regularly' is the definition.
(I've seen this before)
'be sick in back yard' is the wordplay.
'be sick' becomes 'ail' ('ail' can be a synonym of 'be sick'**).
'in' means one lot of letters goes inside another.
'back' shows that the letters should be reversed in order.
'yard' becomes 'yd'.
'yd' backwards is 'dy'.
'ail' inserted inside 'dy' is 'DAILY'.
(Other definitions for daily that I've seen before include "paper, of a sort" , "regularly" , "A rag, perhaps" , "Newspaper; cleaner" , "often" .)