Sparkling brook Scotsman found in Bute, oddly (9)
I believe the answer is:
brilliant
'sparkling' is the definition.
(I've seen this before)
'brook scotsman found in bute oddly' is the wordplay.
'brook' becomes 'rill' (I've seen this before).
'scotsman' becomes 'ian'.
'found in' is an insertion indicator.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
The alternating letters of 'bute' are 'bt'.
'rill'+'ian'='rillian'
'rillian' going into 'bt' is 'BRILLIANT'.
(Other definitions for brilliant that I've seen before include "Very bright; marvellous" , "Brainy" , "Vivid; clever" , "Fantastic!" , "Shining intensly" .)