Officially approve billions? Not so much (5)
I believe the answer is:
bless
'officially approve' is the definition.
(as in giving someone your blessing)
'billions? not so much' is the wordplay.
'billions?' becomes 'b' (abbreviation).
'not so much' becomes 'less' (I've seen this before).
'b'+'less'='BLESS'
(Other definitions for bless that I've seen before include "Render holy" , "Wish happiness" , "Make holy" , "Consecrate; be thankful for" , "Isn't that sweet?" .)