Apostrophe is dividing corporation (5)
I believe the answer is:
tuism
'apostrophe' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'is dividing corporation' is the wordplay.
'dividing' indicates putting letters inside (inserted letters divide the word).
'corporation' becomes 'tum' ('corporation' is a humorous term for stomach fat).
'is' placed into 'tum' is 'TUISM'.
Can you help me to learn more?
(Another definition for tuism that I've seen is " regarding a second person".)