English Synonyms and Antonyms, by James Champlin Fernald
Arms are implements of attack; armor is a defensive covering. The knight put on his armor; he grasped his arms. With the disuse of defensive armor the word has practically gone out of military use, but it is still employed in the navy, where the distinction is clearly preserved; any vessel provided with cannon is an armed vessel; an armored ship is an ironclad. Anything that can be wielded in fight may become a weapon, as a pitchfork or a paving-stone; arms are especially made and designed for conflict.