One day to embellish speech (7)
I believe the answer is:
address
'speech' is the definition.
(synonyms)
'one day to embellish' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'day' becomes 'd' (abbreviation for day).
'to embellish' becomes 'dress' (dressing is a kind of embellishing).
'a'+'d'+'dress'='ADDRESS'
(Other definitions for address that I've seen before include "hail maybe?" , "Give a talk to" , "Form of identification for building" , "Begin to deal with" , "lecture?" .)