Why is the ninth month called September?
reptile, c.1600, "marine tortoise," from French tortue "turtle, tortoise," of unknown origin. The English word is perhaps a sailors' mauling of the French one, influenced by the similar sounding turtle (n.2). Later extended to land tortoises; sea-turtle is attested from 1610s. Turtleneck "close-fitting collar" is recorded from 1895.
"turtledove," Old English turtle, dissimilation of Latin turtur "turtledove," a reduplicated form imitative of the bird's call. Graceful, harmonious and affectionate to its mate, hence a term of endearment in Middle English. Turtledove is attested from c.1300.
To turn upside down; capsize: in the heavier puffs, they thought she would turn turtle
[1860+; fr earlier turn the turtle, found by 1818, referring to making a turtle helpless by turning it on its back]