Gripping object when crossing stream (9)
I believe the answer is:
thrilling
'gripping' is the definition.
(I've seen this before)
'object when crossing stream' is the wordplay.
'object' becomes 'thing' (an object is a thing or item).
'when crossing' means one lot of letters goes inside another.
'stream' becomes 'rill' (rill is a kind of stream).
'thing' placed around 'rill' is 'THRILLING'.
(Other definitions for thrilling that I've seen before include "Causing pleasurable excitement" , "Hair-raising" , "Extremely exciting" , "Gripping" , "Engrossing" .)