abstentionist
/əbˈstɛnʃ(ə)nɪst/ /əbˈstɛnʃənɪst/noun
A person who refrains from exercising his or her vote.
adjective
Characterized by the practise or support of political abstention.
Origin
Mid 19th century; earliest use found in Standard (London). From abstention + -ist, after French abstentionniste, noun and adjective.