The Spanish hipoteca for “mortgage” comes from the Greek hypo- (“down”) and tithenai (“to put, place”). Why? A mortgage is when you put down a deposit, and you put down your commitment to pay it off until it’s all paid down.
From the root tithenai we also get the English… theme. A theme is when you put down one topic you will consistently return to during the course of the event!
This etymology is almost as good as the English equivalent, mortgage… which literally means, pledge until you’re dead. Yup, the same mort- as in death! A mortgage is — literally — what you’ll be paying until you die!