Crossword Genius

Formally call off two arrangements made at the end of May (10)

Ross

I believe the answer is:

officially

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

'formally' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

I've seen this clue in The Irish Times.
Want a hint initially instead of a full solution? Install my app