Small tablet in shed (5)
I believe the answer is:
spill
'shed' is the definition.
(I know that shed can be written as spill)
'small tablet' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'tablet' becomes 'pill' (synonyms).
's'+'pill'='SPILL'
'in' is the link.
(Other definitions for spill that I've seen before include "Allow to drop - fire lighter" , "Cause to fall from horse" , "Let fall accidentally - lighter" , "Waste (liquid)" , "Upset; brim over" .)