Briefly tie soldier’s dog (5)
I believe the answer is:
corgi
'dog' is the definition.
(corgi is a kind of dog)
'briefly tie soldier's' is the wordplay.
'briefly' means to remove the last letter.
'tie' becomes 'cord' (cording is a kind of tiing).
'soldier' becomes 'gi' (GI can mean a US soldier).
'cord' with its final letter taken off is 'cor'.
'cor'+'gi'='CORGI'
(Other definitions for corgi that I've seen before include "Welsh 11" , "Dog of Welsh breed, royal favourite" , "Toy car manufacturer" , "HM's favourite dog" , "Royal canine" .)