This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
contumacious \kon-too-MAY-shuhs\ adj. Obstinate; rebellious; stubbornly disobedient; recalcitrant; persistently, willfully, or openly defiant of authority.
Contumacious is derived from the Latin word contumax, meaning "insolent" or "rebellious."
There are noun forms of the word ("contumacy" and "contumacity"), as well as an adverbial form ("contumaciously").