Bird dog having no lead (5)
I believe the answer is:
eagle
'bird' is the definition.
(eagle is a kind of bird)
'dog having no lead' is the wordplay.
'dog' becomes 'beagle' (beagle is a kind of dog).
'having no lead' means to remove the first letter (the letter which leads the word is removed).
'beagle' with its first letter taken away is 'EAGLE'.
(Other definitions for eagle that I've seen before include "Bird with hooked bill and long broad wings" , "Former US coin" , "Symbolic American bird" , "Symbolic bird of the US" , "The bald one is a US symbol" .)