Essentially admit nothing about rearing falcon (6)
I believe the answer is:
merlin
'falcon' is the definition.
(merlin is a kind of falcon)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for merlin that I've seen before include "Wizard; bird of prey" , "Kind of hawk or Camelot's magician" , "Small falcon; Arthur's friend" , "Small falcon; wizard" , "Magician of the Round Table" .)