Force chaps to infiltrate second corporation (8)
I believe the answer is:
momentum
'force' is the definition.
(I know that momentum is a type of force)
'chaps to infiltrate second corporation' is the wordplay.
'chaps' becomes 'men' (chap means a man).
'to infiltrate' means one lot of letters goes inside another.
'second' becomes 'mo' (both are short periods of time).
'corporation' becomes 'tum' ('corporation' can humorously mean belly fat).
'mo'+'tum'='motum'
'men' going inside 'motum' is 'MOMENTUM'.
(Other definitions for momentum that I've seen before include "Driving force, impetus" , "Impetus gained by a moving object" , "Corbyn supporters" , "driving power" , "Corbynites" .)