Right to support monarch (6)
I believe the answer is:
proper
'right' is the definition.
(associated in meaning)
'support monarch' is the wordplay.
'support' becomes 'prop' (prop up can mean to support).
'monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen).
'prop'+'er'='PROPER'
'to' is the link.
(Other definitions for proper that I've seen before include "Appropriate description" , "Actual" , "Genuine; respectable" , "name someone's given" , "part of Mass" .)