Significatio vocis armus | Babel Free

Definitiones

the shoulder, side; the forequarter; rarely used of humans.

declension-2, masculine

Exempla

“Arma propriē dīcuntur ab armīs, id est humerīs, dēpendentia, ut scūtum, gladius, pūgiō, sīca; ut ea, quibus procul proeliāmur, tēla.”

Arma 'weapons' are, properly speaking, that which hangs from the armī, that is 'shoulders,' such as the shield, sword, dirk, dagger; as are those, by which we fight at a distance, missiles.

Gradus CEFR