Waste second tablet (5)
I believe the answer is:
spill
'waste' is the definition.
(thesaurus)
'second tablet' is the wordplay.
'second' becomes 's' (common abbreviation).
'tablet' becomes 'pill' ('pill' can be a synonym of 'tablet').
's'+'pill'='SPILL'
(Other definitions for spill that I've seen before include "Tip" , "Oil tanker mishap?" , "Thin piece of wood used to light a fire" , "Taper; slop" , "Allow to drop - fire lighter" .)