Sell iodine off as a preservative (7,3)
I believe the answer is:
linseed oil
'a preservative' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe there's an association between them I don't understand?
'sell iodine off' is the wordplay.
'off' indicates anagramming the letters.
'sell'+'iodine'='selliodine'
'selliodine' anagrammed gives 'LINSEED-OIL'.
'as' is the link.
Can you help me to learn more?
(Other definitions for linseed oil that I've seen before include "what's used in making printer's ink" , "for application in sport" , "paint additive?" , "Varnish and paint ingredient" , "Paint/varnish ingredient" .)