Improving and certain to include good growth (7)
I believe the answer is:
upsurge
'growth' is the definition.
(thesaurus)
'improving and certain to include good' is the wordplay.
'improving' becomes 'up' ('up' can be a synonym of 'improving').
'and' says to put letters next to each other.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'to include' is an insertion indicator.
'good' becomes 'g' (abbreviation).
'sure' enclosing 'g' is 'surge'.
'up'+'surge'='UPSURGE'
(Other definitions for upsurge that I've seen before include "Sudden forceful flow from below" , "A rising movement of some intensity" , "growth" , "Hike" , "Rapid rise" .)