Royal seen in county with US soldier and dog (5)
I believe the answer is:
corgi
'dog' is the definition.
(I know that corgi is a type of dog)
'royal seen in county with us soldier' is the wordplay.
'royal' becomes 'r' (abbreviation).
'seen in' means one lot of letters goes inside another.
'county' becomes 'co'.
'with' means one lot of letters go next to another.
'us soldier' becomes 'GI' (GI can mean an American soldier).
'co'+'gi'='cogi'
'r' going inside 'cogi' is 'CORGI'.
'and' acts as a link.
(Other definitions for corgi that I've seen before include "Small Welsh dog with fox-like head" , "Toy car manufacturer" , "Welsh breen of dog" , "Barker?" , "HM's favourite dog" .)