Tempestuous, when your trousers down (8)
I believe the answer is:
thundery
'tempestuous' is the definition.
'your trousers down' is the wordplay.
'your' becomes 'thy' ('thy' historically meant 'your').
'trousers' indicates putting letters inside (to trouser can mean to steal or take).
'down' becomes 'under' (I've seen this before).
'thy' going around 'under' is 'THUNDERY'.
'when' acts as a link.
(Other definitions for thundery that I've seen before include "As storms usually are" , "Oppressive" , "Characterized by rumbles in the sky" , "Sultry" , "Threatening" .)