Jot letter to Grecian (4)
I believe the answer is:
iota
'jot' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for iota that I've seen before include "Old letter" , "Tiny bit" , "Tiny piece" , "Grain" , "A little piece" .)