Serpent takes shelter in the land of Nod (6)
I believe the answer is:
asleep
'in the land of nod' is the definition.
(I've seen this before)
'serpent takes shelter' is the wordplay.
'serpent' becomes 'asp' (asp is a kind of serpent).
'takes' means one lot of letters goes inside another.
'shelter' becomes 'lee' (I've seen this before).
'asp' enclosing 'lee' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Having forty winks" , "(Of a limb) numb" , "In the Land of Nod" , "Dozing" , "coiled up?" .)