A Caledonian, royal on occasion (5)
I believe the answer is:
ascot
'royal on occasion' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'a caledonian' is the wordplay.
'caledonian' becomes 'scot' (I've seen this before).
'a'+'scot'='ASCOT'
Can you help me to learn more?
(Other definitions for ascot that I've seen before include "Type of necktie" , "track" , "Necktie with wide square ends" , "Royal race course" , "English town" .)