arm [OE] Although they may seem connected, arm meaning ‘part of the body’ and arm meaning ‘a weapon’ have had very different routes into English, although they seem ultimately to go back to the same Indo-European root. The former is Old English and thus from a Germanic source, while the latter came into medieval English from French and ultimately Latin arma ‘weapons, armour, military action, implements’. It is also found in armadillo [L16th], from the Spanish for ‘little armed man’; in armistice [L17th] from Latin arma and stitium ‘stoppage’; armour [ME] and armature [M16th], both from Latin armatura and both originally meaning armour. The long arm of the law [M18th] is the police force. Cost or give an arm and a leg seems to be 20th century, but give your right arm for something, meaning ‘to want something very much and be willing to pay a high price for it’ is mid 18th century.