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' means one lot of letters goes inside another (some letters are ringed or contained by others).
'for' becomes 'pro' (as in being 'pro' or in favour of something).
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'esc' going around 'pro' is 'esproc'.
'esproc' written backwards 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" .)