Travel agency may be an established business (5,7)
I believe the answer is:
going concern
'business' is the definition.
(I have seen 'Viable business' mean 'going concern' so perhaps 'business' could also mean 'going concern')
'travel agency may be an established' is the wordplay.
I cannot quite understand how this works, but
'travel' could be 'go' (synonyms) and 'go' is present in the answer.
'agency' could be 'co' (abbreviation for company) and 'co' is located in the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for going concern that I've seen before include "A continuing business" , "profitable business" , "Viable business" , "successful business" , "Thriving business" .)