Suppose old identification number unusable ultimately (5)

I believe the answer is:

opine

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'suppose' is the definition.
(I know that suppose can be written as opine)

'old identification number unusable ultimately' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'identification number' becomes 'pin' (I can't explain this - if you can you should give a lot more credence to this answer).
'ultimately' says to take the final letters.
The final letter of 'unusable' is 'e'.
'o'+'pin'+'e'='OPINE'

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(Other definitions for opine that I've seen before include "Give one's view" , "Express or hold view" , "State one's held view" , "Give opinion" , "Express a point of view" .)

I've seen this clue in The Times.

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