Long-time servant kept short, beginning to remonstrate (8)
I believe the answer is:
retainer
'long-time servant' is the definition.
I can't judge whether this defines the answer.
'kept short beginning to remonstrate' is the wordplay.
'kept' becomes 'retained' (retaining is a kind of keeping).
'short' means to remove the last letter.
'beginning to' says to take the initial letters.
The initial letter of 'remonstrate' is 'r'.
'retained' with its final letter removed is 'retaine'.
'retaine'+'r'='RETAINER'
Can you help me to learn more?
(Other definitions for retainer that I've seen before include "Eritrean (anag)" , "Long-standing family servant" , "Old servant - preliminary fee" , "reduced rent" , "Holding fee or faithful old servant" .)