Exciting object found across stream (9)
I believe the answer is:
thrilling
'exciting' is the definition.
(similar in meaning)
'object found across stream' is the wordplay.
'object' becomes 'thing' (an object is a thing or item).
'found across' is an insertion indicator.
'stream' becomes 'rill' (rill is a kind of stream).
'thing' enclosing 'rill' is 'THRILLING'.
(Other definitions for thrilling that I've seen before include "Causing pleasurable excitement" , "Sensational" , "Engrossing" , "Hair-raising" , "Gripping" .)