Wall is key in storm (5)
I believe the answer is:
gable
'wall' is the definition.
(gable is a kind of wall)
'key in storm' is the wordplay.
'key' becomes 'b' (eg B major, musical key).
'in' indicates putting letters inside.
'storm' becomes 'gale' (I've seen this before).
'b' put within 'gale' is 'GABLE'.
'is' acts as a link.
(Other definitions for gable that I've seen before include "Part of side wall between roofs" , "Part of wall in angle of pitched roof" , "Part of house" , "Triangular upper part of a wall under a roof" , "American actor" .)