Mountaineering aid working after hole (5)
I believe the answer is:
piton
'mountaineering aid' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'working after hole' is the wordplay.
'working' becomes 'on' (e.g. a machine is working or on).
'after' is a charade indicator (letters next to each other).
'hole' becomes 'pit' (pit is a kind of hole).
'on' after 'pit' is 'PITON'.
Can you help me to learn more?
(Other definitions for piton that I've seen before include "Peg used in mountaineering" , "It helps the climber" , "Peg driven into rock in mountain climbing" , "Peg driven into rock as climbing support" , "Metal spike used in rock climbing" .)