Wheel — one damaged side’s eaten by rust, say (7)
I believe the answer is:
oxidise
'wheel' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how they can define each other.
'one damaged side's eaten by rust say' is the wordplay.
'one damaged' becomes 'inthewars' (something that's been 'in the wars' is damaged).
'side's' suggests removing the centre (I've seen 'sides' mean this (only the letters on the sides are used)).
'eaten by' indicates putting letters inside (inserted letters get eaten).
'rust say' becomes 'oxide' (I've seen this in another clue).
'inthewars' with its centre removed is 'is'.
'is' placed within 'oxide' is 'OXIDISE'.
Can you help me to learn more?
(Other definitions for oxidise that I've seen before include "Combine chemically with a particular gas - ie six do (anag)" , "Eg, go rusty" , "Eg, rust (S, not Z)" .)