abstain
Meaning: to freely choose not to commit an action
Usage: Everyone demanded that Angus put on the kilt, but he did not want to do it and abstained.
ascetic
Meaning: practicing restraint as a means of self-discipline, usually religious
Usage: The priest lives an ascetic life devoid of television, savory foods, and other pleasures.
temperance
Meaning: moderation in action or thought
Usage: Maintaining temperance will ensure that you are able to think rationally and objectively.
moderate
Meaning: not extreme; kept within reasonable limits
Usage: Mr. Park supported a moderate proposal because both other plans seemed excessive.
abnegation
Meaning: denial of comfort to oneself
Usage: The holy man slept on the floor, took only cold showers, and generally followed other practices of abnegation.