Person overseas, seeing abdication of Queen, is to say more (9)
I believe the answer is:
expatiate
'is to say more' is the definition.
(to expatiate is to speak or write in detail about)
'person overseas seeing abdication of queen' is the wordplay.
'person overseas' becomes 'expatriate' (someone who lives abroad).
'seeing abdication of' is a deletion indicator (some letters leave or abdicate).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'expatriate' with 'r' taken away is 'EXPATIATE'.
(Other definitions for expatiate that I've seen before include "Go on at length" , "Elaborate" , "In detail, discuss" , "Speak in detail (on)" , "Speak/write in detail (on)" .)