Adjective question

[MarcoTo]

Hello!
I'm a new member! I've started with a test and I didn't understand why is TRUE that
"We can say worthless but not worthful."
Worthful isn't an adjective?

Thank you

[Raymott]

Hello!
I'm a new member! I've started with a test and I didn't understand why is TRUE that
"We can say worthless but not worthful."
Worthful isn't an adjective?

Thank you

Welcome Marco.
I've never heard of 'worthful', though I now see that it is listed in some dictionaries (Did you look?) I wouldn't advise using it though (I don't know where they get some of these words from!)
http://www.thefreedictionary.com/Worthful