Something not wanted soaring round one’s head (5)
I believe the answer is:
onion
'head' is the definition.
(informal term for someone's head or brain)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for onion that I've seen before include "reason for tears" , "Hot dog topping" , "Bulb used as a vegetable" , "Eye-watering vegetable" , "Plant with edible bulb" .)