Low-flying flyer (3)
I believe the answer is:
owl
'flyer' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'low-flying' is the wordplay.
'flying' indicates an anagram (letters fly around into new positions).
'low' is an anagram of 'OWL'.
Can you help me to learn more?
(Other definitions for owl that I've seen before include "Low kind of wise bird" , "Head-swivelling night bird" , "Winged hooter" , "Solemn person" , "Athena's bird" .)