Dog slipping lead is American symbol (5)
I believe the answer is:
eagle
'american symbol' is the definition.
(I've seen this in another clue)
'dog slipping lead' is the wordplay.
'dog' becomes 'beagle' (beagle is a kind of dog).
'slipping lead' means to remove the first letter (I've seen 'slips lead' mean this).
'beagle' with its initial letter removed is 'EAGLE'.
'is' acts as a link.
(Other definitions for eagle that I've seen before include "Former US coin" , "The bald one is a US symbol" , "Bird - emblem of power" , "Two under in 20 across" , "Score of two strokes under par for a golf hole" .)