adjective: Practicing severe self-discipline or self-denial.
noun: One who practices severe self-discipline or self-denial.
From Greek askesis (exercise or training), from askein (to exercise or work).
Earliest documented use: 1646
Usage (from Wordsmith)
“This exhibition of roughly 50 paintings lays out the magpie path that took Mondrian from stolid burgher to ascetic modernist.”
Michael Prodger; From Windmills to Modernism; New Statesman (London, UK); May 30, 2014.