Old male idol admits reading a letter (7)
I believe the answer is:
omicron
'a letter' is the definition.
(I know that omicron is a type of letter)
'old male idol admits reading' is the wordplay.
'old' becomes 'o' (abbreviation).
'male' becomes 'm' (common abbreviation).
'idol' becomes 'icon' (I've seen this before).
'admits' is an insertion indicator.
'reading' becomes 'r' (one of the traditional three R's of education).
'icon' going around 'r' is 'icron'.
'o'+'m'+'icron'='OMICRON'
(Other definitions for omicron that I've seen before include "letter from Athens" , "Foreign letter -- I'm no roc (anag)" , "Olympic character" , "character in Europe" , "A rounded character" .)