Discovered some nice irony in Plato’s letter (7)
I believe the answer is:
omicron
'plato's letter' is the definition.
'omicron' can be an answer for 'letter' (omicron is a kind of letter). I'm not sure about the 'plato's' bit.
'discovered some nice irony' is the wordplay.
'discovered' means to look at the middle letters (dis-covered - outer letters removed).
'some' becomes 'about' (synonyms).
'nice irony' becomes 'micron' (I am not sure about this - if you are sure you should believe this answer much more).
The central letter of 'about' is 'o'.
'o'+'micron'='OMICRON'
'in' is the link.
Can you help me to learn more?
(Other definitions for omicron that I've seen before include "Foreign letter -- I'm no roc (anag)" , "letter from 13 [HELLENE]" , "character in Europe" , "Moronic (anag) - Greek letter" , "Greek short 'o'" .)