noun
Refers to a person who betrays trust, faith, or a cause. Often used in formal or serious contexts.
彼は仲間を裏切った背信者だ。
He is a traitor who betrayed his comrades.
その政治家は国民の信頼を裏切った背信者として非難された。
The politician was condemned as a betrayer who broke the people's trust.
Compound of 背信 (breach of faith) + 者 (person). The exact historical derivation is uncertain, but the word follows a standard Sino-Japanese pattern.