Neon is one (3)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
gas
'neon is one' is the definition.
(I know this)
This is all the clue.
(Other definitions for gas that I've seen before include "Petrol (USA)" , "could be embarrassing for American" , "Hydrogen, for example" , "natural resource" , "eg Helium" .)