adjective. Not repayable; that cannot be paid back.

Is unpayable a word?

That cannot be paid.

Is good will one word?

Goodwill can also be spelled as two separate words, good will, but either way it joins good, from the Old English word for "virtuous," god, and will, in Old English willa, or "wish." So when you wish someone well — when you feel friendly or compassionate — you have goodwill toward that person.