snow-in-summer n 1: annual spurge of western United States having showy white-bracted flower clusters and very poisonous milk [syn: {snow-on-the-mountain}, {ghost weed}, {Euphorbia marginata}] 2: chickweed with hairy silver-gray leaves and rather large white flowers [syn: {love-in-a-mist}, {Cerastium tomentosum}]