Adjective, a person who is controlling, monotone and humourless. A stickler for the rules, one who somehow overrules everyone and is extremely powerful and intimidating to all around them. Fair and just, they won't settle without a fight.
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.