Friend with service in royal house (6)
I believe the answer is:
palace
'royal house' is the definition.
(I've seen this before)
'friend with service' is the wordplay.
'friend' becomes 'pal' (pal is a kind of friend).
'with' says to put letters next to each other.
'service' becomes 'ace' (ace is a kind of service**).
'pal'+'ace'='PALACE'
'in' acts as a link.
(Other definitions for palace that I've seen before include "Castle" , "Head of state's residence" , "See 16" , "Locality round a monarch's official residence" , "Regal mansion" .)