Being professional, not upset readily (6)
I believe the answer is:
pronto
'readily' is the definition.
(thesaurus)
'being professional not upset' is the wordplay.
'being professional' becomes 'pro' (I've seen this before**).
'upset' is an anagram indicator.
'not' with letters rearranged gives 'nto'.
'pro'+'nto'='PRONTO'
(Other definitions for pronto that I've seen before include "Right now, immediately" , "Quickly, amigo" , "Promptly, without delay" , "Immediately, amigo" , "Double quick!" .)