A split in the union (7)

I believe the answer is:

divorce

I'm a little stuck... Click here to teach me more about this clue!

'a split' is the definition.
(split can mean a divorce)

I cannot understand how the rest of the clue works.

(Other definitions for divorce that I've seen before include "Permanent separation" , "Legal end to a marriage" , "Split" , "Get separated" , "End one's marriage" .)

I've seen this clue in The Globe and Mail.

Want a hint initially instead of a full solution? Install my app