Someone on an excursion (7)
I believe the answer is:
tripper
'someone on an excursion' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tripper that I've seen before include "Holidaymaker" , "Person on an excursion" , "Being on holiday" , "Someone out for day" , "person having highly enjoyable experience?" .)