Privy to knowledge finally being combined (2,3)
I believe the answer is:
in one
'being combined' is the definition.
(as in 'all in one')
'privy to knowledge finally' is the wordplay.
'privy to' becomes 'in on' (I've seen this before).
'finally' indicates one should take the final letters.
The last letter of 'knowledge' is 'e'.
'inon'+'e'='IN ONE'
(Other definitions for in one that I've seen before include "united" , "A hole . . . . . is a singular golf score" , "Combined" , "As a single unit" .)