Dormant snake outside shelter (6)
I believe the answer is:
asleep
'dormant' is the definition.
(similar in meaning)
'snake outside shelter' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'outside' indicates putting letters inside.
'shelter' becomes 'lee' (as in lee side, the side sheltered from wind).
'asp' placed around 'lee' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Elapse (anag)" , "Please (anag) - numb" , "this fast?" , "In the arms fo Morpheus" , "Dormant, inactive" .)