Currencies firm for a long time (8)

I believe the answer is:

coinages

'currencies' is the definition.
(coinage is a kind of currency)

'firm for a long time' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'for a long time' becomes 'in ages' (eg 'I haven't seen you in ages').
'co'+'inages'='COINAGES'

I've seen this clue in The Independent.

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