Lower away, poltroon! (6)
I believe the answer is:
coward
'poltroon' is the definition.
(similar in meaning)
'lower away' is the wordplay.
'lower' becomes 'cow' (something which lows - makes cow sounds).
'away' becomes 'ard' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cow'+'ard'='COWARD'
Can you help me to learn more?
(Other definitions for coward that I've seen before include "Composer of "Mad Dogs and Englishmen"" , "Poltroon" , "Noel ..... composed musical 'Bitter Sweet'" , "Scaredy-cat" , "Chicken" .)