Simple to deviate (5)
I believe the answer is:
sheer
I believe this is a double definition.
'simple' is the first definition.
(thesaurus)
'deviate' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for sheer that I've seen before include "needing to change a course" , "Complete" , "Nothing other than" , "sudden change of direction" , "Deviate (from) - vertical" .)