Weigh up old member in custody (7)

I believe the answer is:

compare

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'weigh' is the definition.
(thesaurus)

'up old member in custody' is the wordplay.
'up old' becomes 'o' (common abbreviation eg in OE for Old English. I am not sure about the 'up' bit.**).
'member' becomes 'mp'.
'in' means one lot of letters goes inside another.
'custody' becomes 'care' (I've seen this before).
'o'+'mp'='omp'
'omp' inserted into 'care' is 'COMPARE'.

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(Other definitions for compare that I've seen before include "Look at differences and similarities between (things)" , "Contrast - liken" , "what discriminators do" , "Represent as similar; sounds like emcee" .)

I've seen this clue in The Telegraph.

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