Rocky outcrop to climb — and perish! (3)
I believe the answer is:
rot
'perish' is the definition.
(thesaurus)
'rocky outcrop to climb' is the wordplay.
'rocky outcrop' becomes 'tor' (term for a hill).
'to climb' shows that the letters should be reversed in order (I've seen 'climbing' mean this (in a down clue, letters climb up)).
'tor' backwards is 'ROT'.
'and' is the link.
(Other definitions for rot that I've seen before include "Rhubarb" , "Decay in grotesque way" , "Decay, wither" , "Decay, perish" , "bunk" .)