Layer oddly, ounce after ounce (5)
I believe the answer is:
ozone
'layer' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'oddly ounce after ounce' is the wordplay.
'oddly' means one should take alternating letters.
'after' means one lot of letters go next to another.
'ounce' becomes 'oz'.
The alternate letters of 'ounce' are 'one'.
'one' after 'oz' is 'OZONE'.
Can you help me to learn more?
(Other definitions for ozone that I've seen before include "By sea, you could take in this" , "Seaside air, maybe" , "invigorating British air" , "Bracing air of old, now seen as potentially toxic" , "Atmospheric gas shielding us from ultraviolet radiation" .)