Egg feeding two in Rome completely unknown as a starter (9)
I believe the answer is:
initially
'completely unknown as a starter' is the definition.
I can't tell whether this defines the answer.
'egg feeding two in rome' is the wordplay.
'egg' becomes 'nit' (a nit is an insect egg).
'feeding' indicates putting letters inside (one word is fed by another set of letters).
'two' becomes 'II' (Roman numerals).
'in rome' becomes 'ally' (I am not sure about this - if you are sure you should believe this answer much more).
'nit' going within 'ii' is 'initi'.
'initi'+'ally'='INITIALLY'
Can you help me to learn more?
(Other definitions for initially that I've seen before include "Firstly" , "How laser, for example, was put together" , "At the start" , "At first" , "To begin with" .)