Sure to be above zero (8)
I believe the answer is:
positive
'sure' is the definition.
(similar in meaning)
'be above zero' is the wordplay.
I cannot quite see how this works, but
'be' could be 'sit' (sitting is a kind of being) and 'sit' is present in the answer.
'zero' could be 'o' (O resembles 0) and 'o' is present in the answer.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for positive that I've seen before include "sort of image" , "Confident, very sure" , "Of a number, greater than zero - that's certain" , "Sure, convinced" , "Definite, sure" .)