Big shot touching up back-stabber (5)
I believe the answer is:
viper
'back-stabber' is the definition.
I can't judge whether this defines the answer.
'big shot touching up' is the wordplay.
'big shot' becomes 'vip' (I've seen this in another clue).
'touching' becomes 're' (re can mean touching or regarding).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
're' backwards is 'er'.
'vip'+'er'='VIPER'
Can you help me to learn more?
(Other definitions for viper that I've seen before include "Adder" , "poisonous type" , "A poisonous snake or treacherous person" , "crawler" , "Malicious person" .)