Was very keen, say, to get Greek money (6)
I believe the answer is:
lepton
'greek money' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'was very keen say to' is the wordplay.
I cannot really understand how this works, but
'to' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'get' acts as a link.
Can you help me to learn more?
(Another definition for lepton that I've seen is " Subatomic particle".)