Hear about an animal (4)
I believe the answer is:
hare
'an animal' is the definition.
(I have seen 'Swift animal ' mean 'hare' so perhaps 'animal' could also mean 'hare')
'hear about' is the wordplay.
'about' indicates anagramming the letters.
'hear' is an anagram of 'HARE'.
(Other definitions for hare that I've seen before include "Swift rodent" , "Sect: -- Krishna" , "Sort of rabbit" , "'Swift, long-eared animal (4)'" , "Mammal like a large rabbit" .)