ingratitude; thanklessness
A formal or literary term for failing to show gratitude for a kindness received. Often used in set phrases like 忘恩の徒 (ungrateful person).
I was truly disappointed by his ingratitude.
act of ingratitude; ungrateful act
Compound of 忘 (forget) and 恩 (kindness, favor). The exact historical derivation is uncertain, but the meaning is transparent from its components.