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Pronounced /keer roy-AL/ ¹, the noun kir royale—also kir royal, and with capital initial(s)—designates a drink made from champagne, or sparkling white wine, and crème de cassis.

¹ In simple text respell, which breaks words into syllables, separated by a hyphen; the syllable which carries the primary stress is written in capital letters.

A borrowing from the French masculine noun kir royal, the English noun is composed of:
– the noun kir, designating a drink made from dry white wine and crème de cassis, from the name of Canon Felix Kir (1876-1968), Mayor of Dijon, in Burgundy, who is said to have invented the recipe—cf., below, the explanations in quotation 3;
– the French adjective royale, feminine ² of royal, here meaning: first-rate, exceptional—as in the noun café royale, designating a drink made from black coffee and brandy.

² The reason for the use of the feminine form royale is unclear.

These are, in chronological order, the earliest occurrences of the noun kir royale that I have found:

1-: From Brunch brings on warm glow, by the U.S. food columnist Johnrae Earl, published in the Chicago Tribune (Chicago, Illinois, USA) of Thursday 24^th October 1974 [section 6, page 14, column 1]—however, here, the noun is royale kir:

Serving Sunday brunch is a popular way to entertain, especially during the cold months of the football season.
Almost anything can be served at an elegant brunch. The food should be more lavish than an ordinary breakfast.
And, of course, unlike breakfast, cocktails usually are served with brunch. We would like to suggest a little off-beat brunch this week that we think your guests will enjoy.
You start with a royale kir, a cocktail of moderation that will give you a warm glow but will keep you unsmashed for the remainder of Sunday. […]
[…]
First, here’s the royale kir:

ROYALE KIR
[One drink]
1 champagne glass
1 ice cube
1 teaspoon creme de cassis
5½ ounces chilled champagne

Place ice cube in champagne glass. Add creme de cassis, then the champagne. Serve immediately and repeat as often as necessary.

2-: From an advertisement for The French Restaurant, in Omni International, Atlanta, published in The Atlanta Journal (Atlanta, Georgia, USA) of Friday 27^th February 1976 [page 7-A, column 3]:

You’re invited to stop by and relax for a pleasant moment over a Scotch and soda, Dubonnet or a Kir Royale at The French Bar.

3-: From Jug of wine, by Henry J. Moore, published in The Montreal Star (Montreal, Quebec, Canada) of Saturday 26^th June 1976 [page D-14, column 6]:

For the readers who have inquired as to the origin of Kir: It started many years ago when M. Kir, who was then the Mayor of Dijon in France, concocted a drink in an attempt to stimulate sales of the delicious blackcurrant flavored liqueur for which Dijon is famous.
It quickly spread around France as M. Kir took his drink recipe with him wherever he went.
It has also been called vin blanc cassis but the real name is still Kir. Purists will tell you that it must be made only with dry white burgundy and I am sure being a good Burgundian, M. Kir used nothing else. However, any good dry white wine will do and I have even tried it using a light red wine.
To make good Kir all you need is the Creme de Cassis which can be bought only at the Quebec Liquor Corporation outlets and an inexpensive dry white wine. I use the Bourgogne Blanc imported and bottled by the QLC.
The wine must be very cold and you use one part Cassis to four parts wine. You can mix it ahead of time and keep a bottle in the refrigerator as long as you wish. If you are serving it to the younger set you would be wise to dilute it slightly with a little sparkling water.
If you really want to do things proud, try a Kir Royale. This is made in exactly the same way but using sparkling wine instead of the still variety. Again the sparkling wine should be very dry and very cold.

4-: From The Palm Beach Post (West Palm Beach, Florida, USA) of Thursday 24^th March 1977 [page FN2, column 2]:

Kir Gains Popularity

At a recent White House reception, according to press reports the aperitif wine served before dinner was Kir. This delightful, refreshing drink has been gaining popularity in America in the last decade as a moderate start to a perfect evening. It’s full of flavor, awakens the palate and goes with a wide variety of appetizers.
The essence of the drink is cassis, also known as black-currant liqueur. Its tart-sweet taste marries well with white wine, and that’s Kir. Making it is simplicity itself: Pour five ounces of chilled Chablis into a wine glass, add an ounce of cassis, and you have it. Some people prefer it over ice, or with a splash of soda; both are long-standing variations which taste excellent.
A new drink, also gaining popularity these days, is the Kir Royale, which can add a special touch of elegance to any gathering. Simply pour five ounces of Champagne into a wine glass, and add an ounce of cassis. Don’t stir, as the tiny bubbles will do the mixing for you; just enjoy.