Key rings for climbing can be stiff (6)
I believe the answer is:
corpse
'be stiff' is the definition.
(I've seen this in another clue)
'key rings for climbing' is the wordplay.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'rings' is an insertion indicator (some letters are ringed or contained by others).
'for' becomes 'pro' (as in being 'pro' or in favour of something).
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'esc' enclosing 'pro' is 'esproc'.
'esproc' reversed gives 'CORPSE'.
'can' is the link.
(Other definitions for corpse that I've seen before include "Dead bodies" , "Cadaver, dead person" , "Dead body" , "Roof beam" .)