Overturn small tablet (5)
I believe the answer is:
spill
'overturn' is the definition.
(I've seen this before)
'small tablet' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'tablet' becomes 'pill' ('pill' can be a synonym of 'tablet').
's'+'pill'='SPILL'
(Other definitions for spill that I've seen before include "Cause liquid to overflow" , "Allow to drop - fire lighter" , "Cause liquid to flow from a container" , "Accidentally cause to overflow" , "Slop; a lighter" .)