Gemstone dealer has to drink dairy product (8)
I believe the answer is:
lapidary
'gemstone dealer' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'drink dairy product' is the wordplay.
I cannot really understand how this works, but
'drink' could be 'lap' (to lap is to drink up) and 'lap' is found in the answer.
an anagram of 'dairy' is 'idary' which is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'has to' acts as a link.
Can you help me to learn more?
(Other definitions for lapidary that I've seen before include "using concise language" , "worker in jet? Possibly" , "A cutter of gem-stones" , "Engraver of gems on April day" , "stone worker" .)