The 'denunciation' is the *notice* to terminate or cancel. The latter is a perfectly good EN contract term, contrary to the misguided view of some UK lawyers who claim that it is 'not possible' to cancel a contract cf. the UK Consumer Protection Act 1975.

Using serve for notifier avoids the double-up of 'notifying a notice'.

Note the convention in UN etc. international treaties, originally drafted in FR, using even in EN the term to 'denounce' e.g. the treaty.

IATE' website:

AGRICULTURE, FORESTRY AND FISHERIES, LAW [COM] Full entry
FR dénonciation
EN notice of termination

Résiliation is the actual cancellation, termination - or repudiation, not only by act or omission but express notice. Rescission is arguably not unilateral, but normally mutual or by the court at its 'equitable' discretion in the UK by virtue of the 'equitable doctrine of rescission'.