Servant marks refusal to doff cap (6)
I believe the answer is:
menial
'servant' is the definition.
(I know that menial is a type of servant)
'marks refusal to doff cap' is the wordplay.
'marks' becomes 'M' (former German currency).
'refusal' becomes 'denial' (I've seen this in another clue).
'to doff cap' means to remove the first letter (in a down clue, cap could mean the top letter).
'denial' with its first letter taken off is 'enial'.
'm'+'enial'='MENIAL'
(Other definitions for menial that I've seen before include "(Suitable for) servant of low status" , "(Of work) unskilled" , "Demeaning" , "Subservient, lowly" , "A drudge" .)