Slumbering man encircled by snake (6)
I believe the answer is:
asleep
'slumbering' is the definition.
(similar in meaning)
'man encircled by snake' is the wordplay.
'man' becomes 'lee' (Lee is an example).
'encircled by' indicates putting letters inside.
'snake' becomes 'asp' (asp is a kind of snake).
'lee' placed inside 'asp' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Napping" , "coiled up?" , "in bed?" , "Inattentive; numbed" , "not paying attention" .)