Just the aircraft to worry the enemy (7)
I believe the answer is:
harrier
'enemy' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for harrier that I've seen before include "Bird - dog - plane" , "Long distance runner" , "may get on your back?" , "jump jet" , "Cross-country runner and a hound once used for hunting hares" .)