Formal Opposite:
* Refusal: This implies a direct and formal rejection of the invitation.
* Declination: This is a polite way of saying no to an invitation.
Informal Opposites:
* Rejection: This is a more general term for refusing something.
* Turning down: This is a casual way of saying no to an invitation.
* Ignoring: This means choosing not to respond to the invitation at all.
Other Options:
* Exclusion: This implies that someone was deliberately not invited.
* Banishment: This implies that someone is not allowed to attend.
The best opposite word for "invitation" will depend on the specific situation and the intended meaning.