Ozone, for one (3)
I believe the answer is:
gas
'ozone for one' is the definition.
(ozone is a kind of gas)
This is all the clue.
(Other definitions for gas that I've seen before include "could be embarrassing for American" , "may fill American car" , "State of matter not solid or liquid" , "Something that is neither solid not liquid" , "Substance like air" .)