One anticipates jumping it (3)
I believe the answer is:
gun
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'one anticipates jumping' is the wordplay.
I cannot really see how this works, but
'one' could be 'un' (I've seen this in other clues) and 'un' is found in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for gun that I've seen before include "Artillery piece" , "Platform from which to shoot" , "Arm" , "Hired killer" , "Shooter" .)