A person who doesn't show gratitude or thanks for something good that was done for them.
From Latin 'ingratus' (ungrateful), combining 'in-' (not) and 'gratus' (pleasing), used since medieval times to describe the morally condemned ungrateful.
Ancient philosophers considered ingratitude one of the worst character flaws, worse even than laziness, because it breaks the social contract of reciprocity that holds communities together.
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