The use of the word "condolences", in plural, is more common than "condolence". ... The reason for this habit is unclear, but it resembles our habit to send someone our 'regards', 'best wishes', greetings' (all plural), etc.

Is there a plural for condolence?

Full Definition of condolence

2 : an expression of sympathy —usually plural The bereaved family received many condolences.

Is it proper to say condolence?

“Condolences” is the plural form of the noun “condolence.” A “condolence” is an expression of sympathy that you can use to comfort the listener. You will generally use it when referring to death. However, you can use it in other contexts, too.