Green’s Dictionary of Slang

1. intoxicated by a drug, exhibiting signs of disorientation or being out of touch with reality, following the ingestion of a hallucinogen or of cannabis.

1970		Southern Folklore Quarterly XXXIV 128: People are said to be ‘high,’ ‘stoned,’ or ‘spacy’ when feeling the effect of grass.
1972		Eng. Journal LXI 708: The teacher said, ‘The most important thing about marijuana is that it makes you feel spacey.’.
1989		H. Rawson Dict. of Invective (1991) 369: The use of spaced and spacey to describe people who are out of contact with reality because they are high on drugs.
1997		E. Little Another Day in Paradise 100: Mabel is a classic hippie chick [...] a big flowing dress [...] topped by a very spacey smile.
2003		G. Tate Midnight Lightning 42: Hendrix didn’t turn spacy after one tab of acid too many.
2008		R. Price Lush Life 135: We’ve been driving around all day. I’m a little spacey .

2. exhibiting characteristics reminiscent of those experienced when taking a hallucinogen.

1969		Current Sl. IV:1 15: Spacey, adj. Appearing to be functioning on a higher level than usual.
1977		C. McFadden Serial 42: Sam Stein [...] was now living with the same spacy little chick.
1980		A. Maupin More Tales of the City (1984) 9: His spacy-but-sweet roommate, Mona Ramsey.
1981		A.K. Shulman On the Stroll 15: She had only to open her eyes or step into the street to see the sick and spacey getting rolled.
1989		P. Munro Sl. U. 178: spacy out of touch with reality, airheaded.
1999		Guardian Rev. 20 Aug. 4: She is spacy [...] in a not-all-there sort of way.
2005		B. Hare Urban Grimshaw 36: Greta and I [...] got smashed with Spacey Tracy, her mate.

3. (drugs) of an experience or event, generally disorientating, with or without drugs.

1972		Eble Campus Sl. Oct. 6: spacey – similar to the effects produced by use of drugs: That was a really spacey scene.
1978		Maclean’s (Toronto) 13 Nov. 3: This spacey concept ranks high in the lexicon of political absurdities.
1987		D. Hebdige Cut ’n’ Mix 152: Soon the Rasta themes began to fall away, along with the booming bass and spacey drum work.

4. edgy, nervous.

1996

J. Cameron It Was An Accident 13: Anyone but Noreen I’d be spacy by now reckon it was a hit.