Slip out of gear (7)
I believe the answer is:
undress
'slip' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'out of gear' is the wordplay.
'out of' becomes 'un' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gear' becomes 'dress' (both can mean clothing).
'un'+'dress'='UNDRESS'
Can you help me to learn more?
(Other definitions for undress that I've seen before include "Remove clothes, strip" , "Divest of clothes" , "Sunders (anag)" , "Take one's clothes off" , "Nudity" .)