Sleeping porter losing zero time (7)
I believe the answer is:
dormant
'sleeping' is the definition.
(I know that sleeping can be written as dormant)
'porter losing zero time' is the wordplay.
'porter' becomes 'doorman' (synonyms).
'losing' indicates named letters should be taken away.
'zero' becomes 'O' (O resembles 0).
'time' becomes 't' (abbreviation).
'doorman' with 'o' taken out is 'dorman'.
'dorman'+'t'='DORMANT'
(Other definitions for dormant that I've seen before include "asleep" , "Temporarily inactive, being mordant" , "Sluggish" , "In deep sleep" , "Lethargic" .)