Testudo \Tes*tu"do\, n.; pl. Testudines. [L., from testa the shell of shellfish, or of testaceous animals.]

1. (Zo["o]l.) A genus of tortoises which formerly included a large number of diverse forms, but is now restricted to certain terrestrial species, such as the European land tortoise (Testudo Gr[ae]ca) and the gopher of the Southern United States.

2. (Rom. Antiq.) A cover or screen which a body of troops formed with their shields or targets, by holding them over their heads when standing close to each other. This cover resembled the back of a tortoise, and served to shelter the men from darts, stones, and other missiles. A similar defense was sometimes formed of boards, and moved on wheels.

3. (Mus.) A kind of musical instrument. a species of lyre; -- so called in allusion to the lyre of Mercury, fabled to have been made of the shell of a tortoise.

Source: Webster's Revised Unabridged Dictionary (1913)