The best; of the highest quality. Magnitude refers to the grading of the brightness of stars, the first being the brightest. It has been transferred to other matters since at least the seventeenth century. “Thou liar of the first magnitude,” wrote William Congreve in 1695 (Love for Love, 2.2). Water refers to a system for grading diamonds for their color or luster (the latter being akin to the shininess of water), the best quality again being termed the first. This grading system is no longer used, but the transfer to other matters has survived since the early nineteenth century. Sir Walter Scott’s journal has, “He was a . . . swindler of the first water (1826). Order, which here refers to rank, is probably more often heard today than either of the others. It dates from the nineteenth century. The OED cites “A diplomatist of the first order,” appearing in a journal of 1895. A synonymous term, first rate, originated from the time the Royal Navy’s warships were rated on a scale of one to six, based on their size and the weight of the weapons they carried. By the 1700s this term, along with second-rate, third-rate, and so on, was later transferred to general use, most often as a hyphenated adjective. For example, “He’s definitely a second-rate poet, nowhere near as good as his father.”