Irritable jury's conclusion after trial (5)
I believe the answer is:
'irritable' is the definition.
'jury's conclusion after trial' is the wordplay.
'conclusion' says to take the final letters.
'after' means one lot of letters go next to another.
'trial' becomes 'test' (synonyms).
The last letter of 'jury' is 'y'.
'y' put after 'test' is 'TESTY'.
(Other definitions for testy that I've seen before include "bad temper", "Bad-tempered", "Showing irritation", "Grumpy", "Irritably impatient".)