鸿 is the wild swan goose, an enduring symbol in classical poetry. Two famous uses:
鸿雁 (hóngyàn, wild geese — bringers of letters from afar) and the Sima Qian line
死有重于泰山，
或轻于鸿毛 ('a death may weigh more than Mount Tai, or be lighter than a goose feather'), where
鸿毛 stands for the smallest possible weight.
