Crossword Genius

One of the musketeers has to reform (5)

Ross

I believe the answer is:

athos

'one of the musketeers' is the definition.
(I've seen this before)

'has to reform' is the wordplay.
'reform' indicates an anagram (letters in a new form).
'has'+'to'='hasto'
'hasto' with letters rearranged gives 'ATHOS'.

(Other definitions for athos that I've seen before include "Brave soldier" , "Literary musketeer" , "Dumas musketeer" , "Greek monastic mountain" , "Greek mount; one of the Three Musketeers" .)

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