Box smart during trial (3,5)
I believe the answer is:
tea chest
'box' is the definition.
(tea chest is a kind of box)
'smart during trial' is the wordplay.
'smart' becomes 'ache' ('ache' can be a synonym of 'smart').
'during' means one lot of letters goes inside another.
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'ache' inserted within 'test' is 'TEA-CHEST'.
(Other definitions for tea chest that I've seen before include "box exported from India?" , "Dry container" , "box of gunpowder, say" , "Foil-lined wooden box" , "Box for Earl Grey, perhaps?" .)