Old monarch, kind to be on top (6)
I believe the answer is:
former
'old' is the definition.
(I know that old can be written as former)
'monarch kind to be on top' is the wordplay.
I cannot really understand how this works, but
'monarch' could be 'er' (abbreviation for Elizabeth Regina, British Queen) and 'er' is found within the answer.
'kind' could be 'form' (synonyms) and 'form' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for former that I've seen before include "Of an earlier time" , "not present" , "Old < prior < departed" , "long ago" , "Erstwhile" .)