With right hand, start to open letter from abroad (3)
I believe the answer is:
rho
'letter from abroad' is the definition.
(Greek letter)
'with right hand start to open' is the wordplay.
'with' is a charade indicator (letters next to each other).
'right hand' becomes 'RH' (medical abbreviation).
'start to' indicates taking the first letters.
The initial letter of 'open' is 'o'.
'rh'+'o' is 'RHO'.
(Other definitions for rho that I've seen before include "Greek letter R" , "Gr. letter written as P" , "letter to Athens" , "17th Greek letter" , "Sophocles character" .)