Queen to take off in pursuit of rear admiral? (9)
I believe the answer is:
butterfly
'admiral?' is the definition.
(admiral is a kind of butterfly)
'queen to take off in pursuit of rear' is the wordplay.
'queen' becomes 'ER' (short for Elizabeth Regina ie Queen Elizabeth).
'to take off' becomes 'fly' (I've seen this in another clue).
'in pursuit of' is a charade indicator (letters next to each other) (some letters chase after others).
'rear' becomes 'butt' (synonyms).
'er'+'fly'='erfly'
'erfly' after 'butt' is 'BUTTERFLY'.
(Other definitions for butterfly that I've seen before include "Insect with four coloured wings and feelers" , "Beautiful insect and swimming stroke" , "Insect with large, usually brightly coloured, wings" , "Skipper for instance" , "noted geisha?" .)