Be prone to deceive (3)
I believe the answer is:
lie
I believe this is a double definition.
'be prone' is the first definition.
(I've seen this before)
'deceive' is the second definition.
(to lie is to deceive people)
'to' is the link.
(Other definitions for lie that I've seen before include "Stretch out" , "habitat for animal or bird" , "Perversion of the truth" , "create fiction" , "Disinformation" .)