Jolly old soldier, say, catching cab (9)
I believe the answer is:
exuberant
'jolly' is the definition.
(thesaurus)
'old soldier say catching cab' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'soldier say' becomes 'ant' (soldier is a type of ant).
'catching' is an insertion indicator.
'cab' becomes 'Uber' (Uber is a taxi app).
'ex'+'ant'='exant'
'exant' enclosing 'uber' is 'EXUBERANT'.
(Other definitions for exuberant that I've seen before include "Exeunt bar, being in high spirits" , "Vivacious; effusive" , "Elated" , "High-spirited" , "Enthusiastic" .)