OK a meeting including sweetheart queen (8)
I believe the answer is:
adequate
'ok' is the definition.
(thesaurus)
'a meeting including sweetheart queen' is the wordplay.
'meeting' becomes 'date' (date is a kind of meeting).
'including' is an insertion indicator.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'queen' becomes 'qu' (abbreviation for queen).
'e'+'qu'='equ'
'date' going around 'equ' is 'dequate'.
'a'+'dequate'='ADEQUATE'
(Other definitions for adequate that I've seen before include "Enough to meet a purpose" , "'Satisfactory, acceptable (8)'" , "plenty" , "Passable; enough" , "Sufficient or all right" .)