Strong shelter to west protected by enclosure (6)
I believe the answer is:
steely
'strong' is the definition.
(I've seen this before)
'shelter to west protected by enclosure' is the wordplay.
'shelter' becomes 'lee' (as in lee side, the side sheltered from wind).
'to west' shows that the letters should be reversed in order (the letters are written right to left).
'protected by' indicates putting letters inside.
'enclosure' becomes 'sty' (sty is a kind of enclosure).
'lee' backwards is 'eel'.
'eel' inserted within 'sty' is 'STEELY'.
(Other definitions for steely that I've seen before include "Hard and metallic" , "firm" , "Inflexibly severe" , "Determined; severe" , "Gimlet-eyed" .)