Go astray out of sheer terror (3)
I believe the answer is:
err
'go astray' is the definition.
(thesaurus)
'out of sheer terror' is the wordplay.
'out of' indicates a hidden word.
'ERR' is hidden in the letters of 'sheer terror'.
(Other definitions for err that I've seen before include "Leave the straight and narrow" , "Be mistaken" , "Be incorrect" , "do something you shouldn't" , "Be inaccurate" .)