na-adjective, noun
Refers to a lack of loyalty or faithfulness, often in relationships, duty, or allegiance. Can be used as a noun or adjectival noun (不忠な).
彼の不忠な行為は許せない。
I cannot forgive his disloyal act.
不忠は信頼を壊す。
Disloyalty destroys trust.
Compound of 不 (fu, 'not') and 忠 (chū, 'loyalty'). The kanji combination directly conveys the meaning of disloyalty or infidelity.