Prudence — article left unfinished before breach (6)
I believe the answer is:
thrift
'prudence' is the definition.
(thrift is a kind of prudence)
'article left unfinished before breach' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'left unfinished' means to remove the last letter.
'before' is a charade indicator (letters next to each other).
'breach' becomes 'rift' (I've seen this before).
'the' with its last letter taken away is 'th'.
'th'+'rift'='THRIFT'
(Other definitions for thrift that I've seen before include "Economical management of money or resources" , "Extreme care in spending money" , "Parsimony, penny-pinching" , "Prudence in spending, economical management" , "Plant - saving - economy" .)