Green’s Dictionary of Slang

1. melancholy.

1843		T. Haliburton Sam Slick in England I 259: Yes, John [Bull] is a moony man, that’s a fact, and at the full a little queer sometimes.
1848		Dly Crescent (N.O.) 28 Mar. 1/6: I’ve always heerd that crazy people was somehow afflicted with mooney feelings.
1855		T. Haliburton Nature and Human Nature I 196: I hate poets [...] if you see a he one, you see a mooney sort of man, either very sad or so wild-looking you think he is half-mad.
1867		Morn. Post (London) 9 Oct. 7/2: Nothing was more common than a parcel of attendants to be seen at a funeral, sometimes mad drunk and sometimes moony drunk.

2. drunk.

1842		Manchester Courier 5 Mar. 3/2: Drunk— [...] Moony, Maudlin, Muzzy.
1850		Bell’s Life in Sydney 4 May 1/5: How could I be so spooney / As heed that Scampy Sharp’s advice, and got so precious mooney?
1853		Dickens ‘Slang’ in Household Words 24 Sept. 75/2: For the one word drunk [...] moony, muddled, muzzy, swipey, lumpy, obfuscated [etc.].
1864		London Standard 13 Dec. 3/3: The slang synonyms for mild intoxication are [...] Kisky [...] Moony.
1873		Sl. Dict.
1881		Shields Dly Gaz. 10 Jan. n.p.: For the one word drunk [...] we find mops and brooms [...] moony [...] swipy, lumpy [...] on the ran-tan.
1906		Salt Lake City (UT) 30 Mar. 4/5: He is [...] moony [...] dopey [...] paralyzed.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 215: moony, moppy, drunk. ‘Her father is moony most of the time.’.
1933		‘William Juniper’ True Drunkard’s Delight.

3. sentimentally romantic.

[1861		Hills & Plains I 61: No man, let him be ever so moon-stricken, can express himself in any but the simplest words on the momentous occasion of his proposing].
1865		Dickens Our Mutual Friend (1994) 436: What a mooney godmother you are, after all!
1876		‘George Eliot’ Daniel Deronda (1967) 279: Violent and capricious, or moony and insipid.
1880		Bulletin (Sydney) 31 Jan. 2/3: [She] is a dapper little moony-spoony Rubert.
1890		‘’Arry’s Visit to the Moon’ in Punch Christmas Number in P. Marks (2006) 166: Struck me moony her manner did, Charlie, she hypnertised me with her looks.
1902		A.N. Lyons Hookey 45: Bit silly, ain’t it, me comin’ in moony like that? Thought I was still walkin’ with somebody in the park.
1937		J.M. Cain Serenade (1985) 15: I don’t think there’s ever been a man so moony that a little bit of a chill didn’t come over him as soon as a woman said yes.
1983		S. King Christine 69: She [...] had gotten all moony for John Travolta at eleven.
1999		Observer Rev. 20 June 16: Closely associated with moony seductions.
2001		Week (US) 1 June 25: Like when a moony Lopez pieces together the dandelion puff ball.
2016		T. Robinson Rough Trade [ebook] ‘[G]etting all goddamn moony over a broad you dumped months ago’.

4. (Aus.) idiotic.

[1839		Northern Liberator 16 Feb. 3/3: ‘Moony Madness!’ [...] We request our readers to read the above with attention, especially the second resolution [...] passed [...] a week after the full moon. To ask whether these men are or are not in their senses, would be a useless proceeding].
1903		Sydney Sportsman (Surry Hills, NSW) 7 Jan. 1/3: Take our tip, Master Mooney, and don’t be mooney in taking any more chances like the one you did yesterday.
1924		G.H. Lawson Dict. of Aus. Words And Terms 🌐 MOONEY — To be foolish.
1930		K.S. Prichard Haxby’s Circus 85: He’s a bit moony, and gets on the booze now and then.

5. (US) drug-crazed.

1956

H. Gold Man Who Was Not With It (1965) 240: Sure, a hophead himself, he made a moony wiseness [...] he thought the Grack had sent us back for bargaining.