turtle [M16th] English sailors gave the turtle its name. They probably based it on tortue, an early form of tortoise [LME], from French tortue and Spanish tortuga ‘tortoise’ of uncertain origin. A boat is said to turn turtle [E19th] when it turns upside down, because it then looks a bit like the shell of a turtle, or because it is as helpless as a turtle flipped over on its back, although the expression is found from 1689 for catching turtles on shore by turning them on their backs and rendering them helpless.

The turtle in turtle dove is a completely different word whose ultimate source is Latin turtur, an imitation of the bird’s cooing.