Hear about a creature (4)
I believe the answer is:
rhea
'a creature' is the definition.
(rhea is a kind of creature)
'hear about' is the wordplay.
'about' indicates anagramming the letters.
'hear' is an anagram of 'RHEA'.
(Other definitions for rhea that I've seen before include "Small 'ostrich'" , "Ostrich-like bird - satellite of Saturn" , "New World flightless bird" , "Large S. American bird" , "Moon" .)