Changing gear, in tent, in fun (12)
I believe the answer is:
entertaining
'fun' is the definition.
(similar in meaning)
'changing gear in tent in' is the wordplay.
'changing' is an anagram indicator.
'gear'+'in'+'tent'+'in'='gearintentin'
'gearintentin' is an anagram of 'ENTERTAINING'.
(Other definitions for entertaining that I've seen before include "Delightful" , "Being a host - not 4" , "Providing with amusement" , "Comical" , "Being host - promoting enjoyment" .)