A trial — faulty lasso (6)
I believe the answer is:
lariat
'lasso' is the definition.
('lariat' can be a synonym of 'lasso')
'a trial faulty' is the wordplay.
'faulty' indicates an anagram.
'a'+'trial'='atrial'
'atrial' is an anagram of 'LARIAT'.
(Other definitions for lariat that I've seen before include "A cowboy's rope for catching cattle" , "Long noosed rope used to catch animals" , "Rope to lasso or tether" , "Cowboy's rope (of Spanish origin)" , "Long rope with a noose at the end" .)