Ancient craft spoken of in esoteric terms (5)
I believe the answer is:
argot
'in esoteric terms' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'ancient craft spoken' is the wordplay.
I cannot quite see how this works, but
'craft' could be 'argo' (I have seen 'Old craft' mean 'argo' so perhaps 'craft' could also mean 'argo') and 'argo' is found within the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for argot that I've seen before include "Slang for a groat (5)" , "Groat (anag)" , "Patois for groat" , "Particular group's jargon" , "Specialised language" .)