Senates dispenses with instruments (5)

I believe the answer is:

saxes

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'instruments' is the definition.
(sax is a kind of instrument)

'senates dispenses with' is the wordplay.
'senates' becomes 's' (this might be a standard abbreviation of which I'm unaware).
'dispenses with' becomes 'axes' (I've seen this before).
's'+'axes'='SAXES'

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I've seen this clue in the Sydney Morning Herald.

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