Trouble in the air for hay fever sufferers (6)
I believe the answer is:
pollen
'trouble' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for pollen that I've seen before include "Seed released by plant" , "Fine powder discharged from a plant" , "Fine powder from certain plants" , "What sticks to insects" , "Frequent cause of allergies" .)