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The original meaning of the noun romantasy (plural: romantasies) is: a fantastical or idealised story, situation, etc., involving romance.
This noun now specifically designates a subgenre of fiction that combines elements of both the romance and fantasy genres, typically focused on a romantic narrative that takes place in a fantasy setting. This noun also designates a work in this subgenre.
The noun romantasy is a blend of either the noun romance or the adjective romantic, and of the noun fantasy.
These are, in chronological order, the earliest occurrences of the noun romantasy (plural: romantasies) that I have found:
—Note: It is likely that romantasy has, in the course of time, been coined on separate occasions by various persons, independently from one another:
1-: From an advertisement for Kaufmann’s, a Pittsburgh department store, published in The Pittsburgh Press (Pittsburgh, Pennsylvania, USA) of Wednesday 16th May 1928 [page 24, column 4]:
Now—PINK Willow English Luncheon Ware
Service for 6 5.95 Regularly 6.95
Every hostess knows Blue Willow *, the lovers fleeing across the bridge, the turtle doves and all the other romantasies . . . and now we’ve had this illustrous [sic] pattern done in PINK, and it’s delightful . . . and you’ll want to see it . . . and own it!
Craze-proof, too. Very hard to chip. Easily cleaned, because of the very high glaze. 32 pieces.
* The reference is to Blue Willow, i.e., crockery bearing the willow pattern, that is, a pattern of domestic crockery in blue, originally designed in England in the late 18th century, having willow-trees as a prominent feature.
2-: From an advertisement for When the Cat’s Away (London: J. M. Dent & Sons Ltd, 1940), by the British author Gerald Bullett (1893-1958)—advertisement published in The Observer (London, England) of Sunday 25th August 1940 [page 2, column 6]:
The holiday novel of the year
Bullett versus bombs!
Are we light-hearted? Yes—if we counter warning-weariness by reading Gerald Bullett’s romantasy:
When the cat’s away
GERALD BULLETT
‘It is the lightest of frolics: a delightfully absurd plot, a peer, and a girl who runs away from home, a few eccentrics, and a cat—and frivolous and charmingly witty it all is.’—RALPH STRAUS.
Full-length novel in war format: 7/6.
3-: From Tea Drinking Encouraged To Feed, Shelter Chinese War Orphans, about the American Committee for Chinese War Orphans, by Carmen V. Flournoy, published in The Berkshire Evening Eagle (Pittsfield, Massachusetts, USA) of Tuesday 15th July 1941 [page 12, column 2]:
What more fitting than to sell teas imported from China to aid that country’s innocent unfortunates? Fine China teas are a treat to Americans. At the very least, it’s a fair exchange.
[…]
The teas are well chosen—each has distinctly individual and memorable flavor. Jasmine is the kind one usually thinks of as Chinese tea. Delicate and flower-scented, a sip of it has the power to transport one into swirls of “romantasy.”
4-: From Leaving the cubes behind, by Anne Gordon, published in the Huddersfield Daily Examiner (Huddersfield, Yorkshire, England) of Thursday 28th February 1974 [page 7, column 1]:
Are the cubes and rectangles associated with modern architecture on the way out at last?
Huddersfield architect Mr. Arthur Quarmby, certainly thinks that so far as the domestic scene is concerned, architects in general are having second thoughts, and he has become involved in the “Romantasy” movement; in other words, an attempt to create more varied and even romantic patterns in building.
[…]
[Mr. Quarmby] has even […] drawn plans for a castle near Slaithwaite. With more than a hint of Disneyland in it, it looks like something out of a fairy tale, and though it is a “castle in the air” at present it would certainly provide that element of delight so often missing in present-day building.