Queen in top ten single reversing apathy (7)
I believe the answer is:
inertia
'apathy' is the definition.
(I've seen this before)
'queen in top ten single reversing' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'in' means one lot of letters goes inside another.
'top' becomes 'ai' (I've seen this in other clues).
'single' becomes 'i' (one).
'reversing' says the letters should be written backwards.
'ai'+'ten'+'i'='aiteni'
'r' placed into 'aiteni' is 'aitreni'.
'aitreni' written backwards gives 'INERTIA'.
(Other definitions for inertia that I've seen before include "Lack of movement" , "Display laziness" , "Apathy" , "Stillness" , "Slowness to act, lack of strength" .)