Without a mathematical sign (5)
I believe the answer is:
minus
This might be a double definition.
'without' is the first definition.
(minus means without)
'a mathematical sign' is the second definition.
'minus' can be an answer for 'sign' (minus sign is a kind of sign). I am not sure about the 'a mathematical' bit.
Can you help me to learn more?
(Other definitions for minus that I've seen before include "Negative sign - negative thing" , "deficiency" , "Less, without" , "Lacking; below zero" , "Lacking; negative" .)