Noun
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 Graeca) and the gopher of the Southern United States.
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.
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 dictionaryFamously, the Romans used their shields to create a tortoise-like formation called a testudo in which entire groups of soldiers would be enclosed in an armoured box to provide protection against missiles. Source: Internet
This structure moved so slowly, however, that he called it the testudo (the Latin word for "tortoise"). Source: Internet