noun
disloyal person; traitor
Refers to a person who betrays trust or loyalty, often in a feudal, organizational, or personal context. Somewhat formal or literary.
彼は主君を裏切った不忠者として歴史に名を残した。
He went down in history as a disloyal person who betrayed his lord.
組織にとって不忠者は許されない存在だ。
A disloyal person is unforgivable to the organization.
Compound of 不忠 (disloyalty) and 者 (person). The exact historical derivation is uncertain, but the word follows a standard Sino-Japanese pattern for describing a person with a certain trait.