Completely articulate -- and lively after vacation (7)
I believe the answer is:
utterly
'completely' is the definition.
(synonyms)
'articulate and lively after vacation' is the wordplay.
'articulate' becomes 'utter' (both can mean to say something).
'and' means one lot of letters go next to another.
'after vacation' means to remove the middle letters (the inside letters must vacate).
'lively' with its middle taken out is 'ly'.
'utter'+'ly'='UTTERLY'
(Other definitions for utterly that I've seen before include "Downright" , "unqualified" , "Completely and without qualification" , "Absolutely and completely" , "Completly and without qualification" .)