Epsom's leading character, say, repeatedly backing a horse (3-3)

'a horse' is the definition.
(gee-gee is a kind of horse)

'epsom's leading character say repeatedly backing' is the wordplay.
'say repeatedly' means three replacements for 'say'.
'leading character' says to take the initial letters.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'say' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'backing' says the letters should be written backwards.
The initial letter of 'epsom' is 'e'.
'e'+'eg'+'e'+'eg'='eegeeg'
'eegeeg' reversed gives 'GEE-GEE'.

Can you help me to learn more?