Competent English Queen participating in an engagement (8)
I believe the answer is:
adequate
'competent' is the definition.
('adequate' can be similar in meaning to 'competent')
'english queen participating in an engagement' is the wordplay.
'english' becomes 'e' (abbreviation).
'queen' becomes 'qu' (**).
'participating in' indicates putting letters inside.
'an' becomes 'a'.
'engagement' becomes 'date' ('date' can be a synonym of 'engagement').
'e'+'qu'='equ'
'a'+'date'='adate'
'equ' placed inside 'adate' is 'ADEQUATE'.
(Other definitions for adequate that I've seen before include "'Good enough, all right (8)'" , "Enough to meet a purpose" , "Just about sufficient, acceptable" , "Passable but not great" , "Sufficient or all right" .)