Question

Does a compound word have to be a noun, or can it be an adjective?

Answer 1

A compound word may be whatever part of speech you wish according to the function it serves.

Explanation:

Some examples:
Absentminded people should take care when they dress - adjective.
Absentmindedness is common among elderly persons - noun
He absentmindedly forgot to zip up his trousers. - adverb