Most of cabinet one saw united (12)
I believe the answer is:
consolidated
'united' is the definition.
(consolidating is a kind of uniting)
'most of cabinet one saw' is the wordplay.
'most of' means to remove the last letter.
'cabinet' becomes 'console' ('console' can be a synonym of 'cabinet').
'one' becomes 'i' (Roman numeral).
'saw' becomes 'dated' ('date' can be a synonym of 'see'**).
'console' with its last letter taken off is 'consol'.
'consol'+'i'+'dated'='CONSOLIDATED'
(Other definitions for consolidated that I've seen before include "made stronger?" , "made more secure" , "Combined into a single unit" , "United" .)