Nervously trail a rope (6)
I believe the answer is:
lariat
'rope' is the definition.
(lariat is a kind of rope)
'nervously trail a' is the wordplay.
'nervously' indicates an anagram.
'trail'+'a'='traila'
'traila' is an anagram of 'LARIAT'.
(Other definitions for lariat that I've seen before include "Rope used as a lasso" , "Cattle-catching rope" , "Rope to lasso or tether" , "A trail (anag) - rope" , "A cowboy's rope used to tether a horse" .)