Recently a professor in my department got injured in a car accident and I want to write him a sympathy email. However, I don't know how to choose the title/subject for the email. Can I simply write "condolence"? (Is it only used for those who passed away?) If it is okay to use "condolence", are there any alternative to it?
Condolence is usually reserved for expressions of sympathy for the bereaved. Cambridge Dictionary defines condolence as "sympathy and sadness for the family or close friends of a person who has recently died, or an expression of this, especially in written form". For an injury, another word would be better. Sympathy might be a good candidate. In general, genuine messages of this type do not strive for dictionary correctness; we are showing sympathy, not showing off our command of language. I suggest a simple subject line like "Sorry to hear about your accident".