Sovereign gold (1000kg) ring on tailless rodent (10)
I believe the answer is:
autonomous
'sovereign' is the definition.
(synonyms)
'gold 1000kg ring on tailless rodent' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
't000kg' becomes 'to' (I can't explain this - if you can you should believe this answer much more).
'ring' means one lot of letters goes inside another.
'tailless' means to remove the last letter (the tail of the word is removed).
'rodent' becomes 'mouse' (mouse is a kind of rodent).
'to' enclosing 'on' is 'tono'.
'mouse' with its final letter taken off is 'mous'.
'au'+'tono'+'mous'='AUTONOMOUS'
Can you help me to learn more?
(Other definitions for autonomous that I've seen before include "Independent" , "Self-governing" .)