Add to company millions (sterling) (8)

I believe the answer is:

compound

'add to' is the definition.
(thesaurus)

'company millions sterling' is the wordplay.
'company' becomes 'co' (abbreviation).
'millions' becomes 'm' (abbreviation).
'sterling' becomes 'pound'.
'co'+'m'+'pound'='COMPOUND'

(Other definitions for compound that I've seen before include "Add on to" , "Exacerbate - enclosure" , "Enclosed area - not simple!" , "Make worse; property enclosure" , "Blended substance - enclosed area" .)

I've seen this clue in The Telegraph.

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