Hostile and hospitality are siblings who went in opposite directions. Both trace to Proto-Indo-European *ghos-ti-, meaning 'stranger' or 'guest.' In early Latin, hostis preserved this neutral sense — a hostis was simply someone from outside. But as Rome grew and its borders became contested, hostis darkened: by classical times it meant 'enemy' exclusively. The welcoming sense survived in a different Latin branch: hospes ('host, guest'), which generated hospitality, hospital, hostel, and hotel. Latin hostilis ('of or pertaining to an enemy') was the adjective form of the now-adversarial hostis. French inherited it, and English borrowed it in the 1580s. The semantic split between hostile and hospitable may reflect a genuine tension in ancient societies: strangers could be either guests to welcome or threats to repel, and you often did not know which until they arrived. Roman law eventually formalised the distinction — a hostis was a public enemy of the state, while a peregrinus was a peaceful foreigner. The word 'hostage' also belongs to this family, originally meaning a person handed over as a guarantee of good faith between host and guest.