Stormy result, by mistake (8)
I believe the answer is:
blustery
'stormy' is the definition.
(similar in meaning)
'result by mistake' is the wordplay.
'mistake' is an anagram indicator.
'result'+'by'='resultby'
'resultby' is an anagram of 'BLUSTERY'.
(Other definitions for blustery that I've seen before include "Talking loudly and aggressively to little effect" , "Somewhat windy" , "Sly brute (anag)" , "Spasmodically windy" , "Boastful" .)