Rat's tail carried by parrot, one in calm state (2,5)
I believe the answer is:
at peace
'calm state' is the definition.
'at peace' can be an answer for 'calm' (I've seen this in another clue). I am not sure about the 'state' bit.
'rat's tail carried by parrot one' is the wordplay.
'tail' says to take the final letters.
'carried by' means one lot of letters goes inside another.
'parrot' becomes 'ape' (both can mean to imitate).
'one' becomes 'ace' (ace has a value of one in some card games).
The final letter of 'rat' is 't'.
't' placed into 'ape' is 'atpe'.
'atpe'+'ace'='AT PEACE'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for at peace that I've seen before include "no longer with us" , "calm" , "Dead?" , "pushing up the daisies" , "Not disputing" .)