Emperor going round old country could be positive or negative (3-4)
I believe the answer is:
non-zero
'be positive or negative' is the definition.
(I've seen this before)
'emperor going round old country' is the wordplay.
'emperor' becomes 'nero' (Roman emperor).
'going round' indicates putting letters inside (some letters go around others).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'country' becomes 'nz' (abbreviation for New Zealand).
'o'+'nz'='onz'
'nero' enclosing 'onz' is 'NON-ZERO'.
'could' acts as a link.
(Other definitions for non-zero that I've seen before include "Having a positive or negative value, ie anything not equating to nought (mathematics)" , "Either positive or negative" .)