Dormant snake seen outside shelter (6)
I believe the answer is:
asleep
'dormant' is the definition.
(similar in meaning)
'snake seen outside shelter' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'seen outside' is an insertion indicator.
'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 "this fast?" , "Having forty winks" , "Dozing" , "out like a light?" , "In the Land of Nod" .)