This very long-standing term now means that two parties have historically had a dislike for one another, and any new conflict has no effect one way or the other. In centuries past, unrequited love was viewed as ‘lost,’ so that is how it was originally denoted, meaning that two individuals or groups either loved or hated each other to the same degree. The earliest known citation in print is from a play attributed to Shakespeare, though some question his authorship, from 1592, A Faire Em, Act V, Scene i:

“And never could I see a man, methought, That equaled Manville in my partial eye. Nor was there any love between us lost, But that I held the same in high regard…”

Then in 1637, this reference was made in another play, The Miseries of Enforced Marriage by George Wilkins, Act V:

“Ilf. And there shall be no love lost, nor service neither, Ile doe thee service at board, and thou shalt doe me service at bed.”

In the 19th century the meaning seemed to alter a bit toward what it is in our day, not necessarily reflecting either intense love or zealous hate; only a common aversion. In describing the feelings between a city politician and the editor of the London Times, William Hazlitt, in Political Essays with Sketches of Public Figures, 1819, writes on page 168:

“There is no love lost between them. He does not leave them the sole benefit of their old motto, Odia in longum jaciens qua, conderet auctaque promeret. He makes neither peace nor truce with them.”