Spoken half of Scottish royal castle (4)
I believe the answer is:
oral
'spoken' is the definition.
(similar in meaning)
'half of scottish royal castle' is the wordplay.
'half of' means to take half the letters.
'scottish royal castle' becomes 'balmoral' (I've seen this before).
'balmoral' cut in half is 'ORAL'.
(Other definitions for oral that I've seen before include "Said - form of test" , "Type of exam" , "Of the voice" , "Spoken test" , "By word of mouth (4)" .)