Low fellow keeping high status to the bitter end (5)
I believe the answer is:
viper
'low fellow' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'high status to the bitter end' is the wordplay.
'high status' becomes 'vip' (I am not sure about this - if you are sure you should believe this answer much more).
'end' suggests the final letters.
The final letters of 'the bitter' are 'er'.
'vip'+'er'='VIPER'
'keeping' is the link.
Can you help me to learn more?
(Other definitions for viper that I've seen before include "Venomous snake, person" , "spiteful person" , "A small poisonous snake" , "A poisonous snake or treacherous person" , "Deadly-venomous snake" .)