Soldier hiding a stone in royal house (9)
I believe the answer is:
lancaster
'royal house' is the definition.
(Lancaster is an example)
'soldier hiding a stone' is the wordplay.
'soldier' becomes 'lancer' (lancer is a kind of soldier).
'hiding' indicates putting letters inside.
'stone' becomes 'st'.
'a'+'st'='ast'
'lancer' placed around 'ast' is 'LANCASTER'.
'in' is the link.
(Other definitions for lancaster that I've seen before include "City in north-west England" , "John of Gaunt?" , "City of NW England" , "University" , "Historical English royal house with the emblem of a red rose" .)