Male in loosest pants, still (10)
I believe the answer is:
motionless
'still' is the definition.
(synonyms)
'male in loosest pants' is the wordplay.
'male' becomes 'm' (common abbreviation).
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'in'+'loosest'='inloosest'
'inloosest' with letters rearranged gives 'otionless'.
'm'+'otionless'='MOTIONLESS'
(Other definitions for motionless that I've seen before include "Still, unmoving" , "Perfectly still" , "Immobile" , "constipated?" , "not having anything to vote about?" .)