Gas, one from Australia? (5)
I believe the answer is:
ozone
'gas' is the definition.
(I know that ozone is a type of gas)
'one from australia?' is the wordplay.
'one from' becomes 'o' (I've seen this in other clues).
'australia?' becomes 'zone' (I can't justify this - if you can you should give a lot more credence to this answer).
'o'+'zone'='OZONE'
Can you help me to learn more?
(Other definitions for ozone that I've seen before include "A gas; threatened layer in air" , "Sea air (found in layer?)" , "invigorating British air" , "Form of oxygen in earth's upper atmosphere - there's a hole in it" , "Gas formed from oxygen" .)