Without being a bit amusing, maybe (5)
I believe the answer is:
minus
'without' is the definition.
(minus means without)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for minus that I've seen before include "Take-away (sign)" , "Negative arithmetic operation" , "Lacking; negative" , "Disadvantage" , "deficiency" .)