They're probably looking for false, but to be honest, I use it in my writing sometimes. It depends on the setting and character, or it should be specified as slang in nonfiction writing.
1. suffix-less meaning- not helpful
2. suffix-ly meaning- going fast
3. suffix-ful meaning- hurting and object
4. suffix-less meaning- not thinking/ or uh idk
i really do hope this helped :)
