Horse arrives with one before queen's runner (7)
I believe the answer is:
harrier
'runner' is the definition.
(I've seen this before)
'horse arrives with one before queen's' is the wordplay.
I cannot quite see how this works, but
'horse' could be 'h' (abbreviation as in horse power) and 'h' is located in the answer.
'arrives' could be 'arr' (abbreviation used in transport) and 'arr' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'before' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'queen' could be 'r' (abbreviation for regina, e.g. in ER ) and 'r' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for harrier that I've seen before include "Hare hound" , "Short-winged hawk" , "Bird - dog - plane" , "Cross-country runner and a hound once used for hunting hares" , "that flies!" .)