When someone gets a bruise on their elbow, but insists on going to a doctor because they are scared it may be something as serious as cancer or gangrene
Alex fell and hit his elbow while trying to retrieve a football, and that elbowlina decided to go see a doctor
When some resigns or retires from a job, they are on "eternity leave". This can also refer to someone who has passed away, especially someone who worked somewhere for a long time, retired/resigned, then passed away later.
Oh I'm sorry, you didn't know that Kelly is on eternity leave? She resigned and moved to Hawaii!
With regrets I would like to inform you that my boss is officially on eternity leave. I will never see or hear them again. Ever.