Apostrophe is dividing corporation (5)
I believe the answer is:
tuism
'apostrophe' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'is dividing corporation' is the wordplay.
'dividing' is an insertion indicator (inserted letters divide the word).
'corporation' becomes 'tum' ('corporation' can humorously mean belly fat).
'is' placed within 'tum' is 'TUISM'.
Can you help me to learn more?
(Another definition for tuism that I've seen is " regarding a second person".)