Feign, affect (9)
I believe the answer is:
dissemble
This clue is a double definition.
'feign' is the first definition.
(synonyms)
'affect' is the second definition.
(I know that affect can be written as dissemble)
(Other definitions for dissemble that I've seen before include "Conceal one's true feelings" , "Disguise one's true feelings" , "Hide true motives" , "Hide one's true feelings" , "Conceal or disguise feelings or motives" .)