Chestiest is an adjective that describes someone or something excessively proud or boastful. Antonyms for chestiest would be humble, modest, unpretentious, self-effacing, and reserved. A humble person is modest and unassuming, and they don't draw attention to themselves or their successes. A modest person is unassuming, free from extravagance, and does not attract attention to their accomplishments. An unpretentious person is modest and genuine, without any airs or pretensions of being more important than they are. A reserved person is quiet and restrained, keeping their thoughts and feelings to themselves. In contrast, chestiness could easily be replaced by any of these qualities.