'armadillo' originates from Spanish, specifically the word 'armadillo' (a diminutive of 'armado') meaning 'little armored (one)', ultimately from Latin 'armatus' (past participle of 'armare', to arm) and 'arma' meaning 'arms'.

English borrowed 'armadillo' from Spanish (and Portuguese) in the 17th century after European contact with the Americas; the Spanish word itself derives from a diminutive of 'armado' ('armored'), which traces back to Latin roots.

Initially it meant 'little armored one' (a descriptive name), and over time it came to specifically denote the New World mammal we now call an 'armadillo'.