Less dash! (5)
I believe the answer is:
minus
'less' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for minus that I've seen before include "deficiency" , "Disadvantage" , "Deprived of" , "Lacking; below zero" , "Negative sign - negative thing" .)