first magnitude/order/water, of the

of the first magnitude

Of major importance or significance. You have to study Shakespeare because he is a poet of the first magnitude. We need to close the highway immediately—this is an accident of the first magnitude.
See also: first, magnitude, of

of the first order

Of the greatest importance, significance, or magnitude. You have to study Shakespeare because he is a poet of the first order. We need to close the highway immediately—this is an emergency of the first order.
See also: first, of, order

of the first water

Of the best quality; having the utmost skill or value. An allusion to the old system of grading diamonds, the most brilliant of which were deemed "of the first water." She is a lady of the first water—dignified, well spoken, and with unimpeachable integrity. The restaurant is renowned for serving food of the first water.
See also: first, of, water

of the first water

Fig. of the finest quality. This is a very fine pearl—a pearl of the first water. Tom is of the first water—a true gentleman.
See also: first, of, water

of the first water

Of the finest quality, as in That was a play of the first water. This idiom refers to a grading system for diamonds for their color or luster (compared to the shininess of water). The system is no longer used but the term, used figuratively since the early 1800s, has survived it.
See also: first, of, water

of the first water

OLD-FASHIONED
You can use of the first water after a noun to mean that someone is very good at something or is an extreme example of something. Jocelyn had proved herself to be a leader of the first water. He was full of energy, Janet recalled, an eccentric of the first water. Note: The brilliance of a diamond is called its water. Diamonds `of the first water' are of very high quality.
See also: first, of, water

of the first order (or magnitude)

used to denote something that is excellent or considerable of its kind.
In astronomy, magnitude is a measure of the degree of brightness of a star. Stars of the first magnitude are the most brilliant.
See also: first, of, order

of the first water

extreme or unsurpassed of kind.
The sense of water referred to in this expression is ‘the quality of brilliance and transparency of a diamond or other gem’: if a diamond or pearl is of the first water it possesses the greatest possible degree of brilliance and transparency. In its transferred use, however, the phrase often refers to someone or something regarded as undesirable, e.g. a bore of the first water .
See also: first, of, water

first magnitude/order/water, of the

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.”
See also: first, magnitude, of, order