HOST, HOSPE, a term of mutual relation, applied both to a person who lodges and entertains another, and to the person thus lodged. It is formed from the Latin hospes, which according to some, was thus called quasi hostium or ostium petens, ostium having anciently been written with an aspirate. Thus the innkeeper says, he has a good host, in speaking of the traveller who lodges with him; and the traveller, again, says he has a kind host, in speaking of his landlord.
It must be observed, however, that it was the custom amongst the ancients, when any stranger asked lodging, for the master of the house, and the stranger, each of them to set a foot on their own side of the threshold, and swear they would neither of them do any harm to the other. It was this ceremony which raised so much horror against those who violated the law or right of hospitality on either side, inasmuch as they were looked upon as perjured.
Instead of hospes, the ancient Latins called it hostis, as Cicero himself informs us; though, in course of time, hostis came to signify an enemy, so much had the notion of hospitality degenerated.