Red-breasted Merganser

Mergus serrator

Serrator means 'sawyer,' for the saw-like edges on its bill that grip slippery fish. It's the same root as 'serrated,' as in a serrated knife.

Mergus was a Roman name for a water bird, from mergere, 'to dive'; 'merganser' joins it with anser, 'goose,' so it's a 'diving goose.' Serrator comes from serra, 'saw.' Only breeding males show the red breast.