an act of swallowing something, especially food or drink. "he downed his drink in one swallow" a migratory swift-flying songbird with a forked tail and long pointed wings, feeding on insects in flight. "The central aim of our study was to demonstrate that both natural and sexual selection have been important in shaping the tail streamer of the barn swallow ." verbean act of swallowing something, especially food or drink. "he downed his drink in one swallow" a migratory swift-flying songbird with a forked tail and long pointed wings, feeding on insects in flight. "The central aim of our study was to demonstrate that both natural and sexual selection have been important in shaping the tail streamer of the barn swallow ." verbe