Green’s Dictionary of Slang

frat n.

[abbr.]
(US)

1. a college fraternity; also attrib.; thus frat house, frat-pin etc.

[US]W.C. Gore Student Sl. in Cohen (1997) 7: Frat n. A fraternity; a member of a fraternity.
[US]Cornhusker 24 Nov. in DN IV:ii 129: Frats pledge unsuspecting Freshmen.
[US]Ade Knocking the Neighbors 226: [He] could not quite make up his Mind whether to join a High School Frat or go on the stage.
[US]S. Lewis Arrowsmith 35: This ole frat’ll never have another goat like Fatty.
[US]H.W. Brecht Downfall 185: Morrison’s showing your frat-pin to the whole freshman class.
[US](con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 354: The fellows in my frat [...] they’re all swell fellows.
Duckett ‘Double Feature’ in N.Y. Age 22 Jan. 7/1: [H]e is on the look out for a girl friend to go with his frat pin.
[US]Flash! (Wash., D.C.) 3 Jan. 18/2: Swing Sessions, an outgrowth of the currently popular music played by the ‘jam units’ have outmoded to an extent the former type of close ‘bunny-hug’ dancing that was the bane of frat house hops.
[US](con. 1944) N. Mailer Naked and Dead 552: At the State University he is accepted in a good frat.
[Can]M. Richler Apprenticeship of Duddy Kravitz (1964) 168: Every time they take him into one of their frat houses he practically licks their boots.
[US]R. Gover One Hundred Dollar Misunderstanding 9: It was the weekend of the big frat formal.
[US]H. Rap Brown Die Nigger Die! 16: My loyalty is to my Frat., God, and my country, in that order.
[US]E. Thompson Garden of Sand (1981) 430: Melding the high shriek of women [...] with the cracked ‘old boy’ baritones of college frat houses.
[UK]J. Carr Bad (1995) 20: Some flattop frat dude with a dumb look.
[Can]M. Atwood Cat’s Eye (1989) 209: She goes to frat parties.
[US]C. Hiaasen Stormy Weather 7: Webo Drake glanced worriedly at his frat brother.
[US]B. Wiprud Sleep with the Fishes 53: A notch up from beer slides at a frat wing-ding.
[US]C. Buzzell My War (2006) 11: Joining the Marines was like joining a party frat with weapons.
[US]B. Coleman Rakim Told Me 119: Using a sample swiped from the Troggs’ frat rock evergreen ‘Wild Thing’ .
[UK]Guardian G2 11 Mar. 5/1: A video surfaced of frat members singing a racist chant.

2. (also frat boy, ...brother, ...bull, ...head, ...man) a member of a fraternity; thus non-frat.

[US]W.C. Gore Student Sl. in Cohen (1997) 8: Frat (n.) A fraternity; a member of a fraternity .
[US]E.H. Babbitt ‘College Words and Phrases’ in DN II:i 36: frat, n. A member of a fraternity. [Ibid.] 46: non-frat, n. One who is not a member of a fraternity.
[US]Ladies’ Home Journal Nov. 19/1: In the ‘co-ed’ ’varsities the ‘frats’ and sororities pair off just as brothers and sisters do in a large family [DA].
[US]S. Lewis Arrowsmith 28: I’m going to expose Clawson even if he is a frat-brother of mine.
[UK]M. Terry Old Liberty (1962) 21: Say, swell. Or did we tongue it, big frat man?
[US]K. Kolb Getting Straight 84: Pete and I were old undergrad frat brothers.
[US]S. Greenlee Spook who Sat by the Door (1972) 14: Where’d you go to school, man? [...] You frat?
[US]L. Bangs in Psychotic Reactions (1988) 33: Dope out with the gang, grass, speed, reds, Romilar, who cares, some frat bull’s gonna buy us beer.
[US]Eble Campus Sl. Spring 2: frat – a male in a fraternity or in a military organization.
[US]Eble Campus Sl. Oct. 4: frathead – stereotypic fraternity member.
[US]S. Morgan Homeboy 137: The largest of the frat boys [...] slung his drink at her.
[US]G. Pelecanos Shame the Devil 148: The Black Cat was [...] spartan like the old 9:30 but without the new 9:30’s frat-boy crowd.
[US]T. Dorsey Stingray Shuffle 17: Frat brothers in a Jeep that said No Fear!
[UK]G. Iles Turning Angel 344: I’m going to give those frat boys the ride of their lives!
[US]A. Steinberg Running the Books 55: She behaved like a frat boy, displayed little to no socialization.
[US]P. Beatty Sellout (2016) 8: Some buffed ancient Greek frat boy.
[US](con. 1962) J. Ellroy Enchanters 41: Frat boys golf-carted guests.

In derivatives

fratastic (adj.) [-tastic sfx]

(US campus) pertaining to fashions as espoused by a member of a fraternity.

[US]Eble UNC-CH Campus Sl. 2011 4: FRATASTIC — fraternity + fantastic epitomizing the wardrobe and behavior associated with fraternity members: ‘He’s so fratastic in his silk bowtie and pastel shorts—and he’s probably wearing Vineyard Vines underwear.’ Also FRAT DADDY, FRAT STAR.
fratdom (n.) [sfx -dom]

(US campus) the world of fraternities.

Ace Weekly 19 Aug. 🌐 The University’s expansion seems to have no bounds, and in this case, little public input. Many homes of historic value lie in the path of future fratdom.

In compounds

frat dick (n.) (also frat fag) [dick n.1 (10)/fag n.4 (2)]

(US campus) a derog. description of a typical fraternity member.

[US]P. Munro Sl. U. 82: frat dick/frat fag member of fraternity who drinks a lot, womanizes, and has an elitist attitude about his fraternity.
frat rat (n.) (also frat brat, ...star) [sense 1 + SE rat/boy/star]

(US campus) a member of a fraternity.

[US](con. WWII) ‘Weldon Hill’ Onionhead (1958) 27: Who the hell could compete with ninetypseve tuxedoed frat rats and a goddam horse?
[US]Poston ‘Problems in the Study of Campus Sl.’ in AS XXXIX:2 118: One may mention cheat sheet ‘notes which a student illicitly brings to an examination’ and frat-rat ‘fraternity man’ (contemptuously viewed).
[US](con. late 1940s) E. Thompson Tattoo (1977) 464: After consulatation one of the frat-rats called back, ‘OK’.
[US]P. Munro Sl. U. 83: frat rat/frat brat/frat boy member of a fraternity.
[US]Eble Campus Sl. Apr.
[US]Eble Campus Sl. Apr. 3: frat star – male college student who dresses in accordance with the stereotype associated with fraternities.
[US]C. Eble UNC-CH Campus Sl. Spring 2016 4: FRAT STAR — the epitome of fraternity culture: ‘That guy looks like he rolled out of a J. Crew catalog—a total frat star’.

In phrases

frat out (v.)

(US campus) to dress and act like a fraternity member.

[US]Eble Campus Sl. Apr. 2: frat-out – to dress in khaki pants, La Costa shirt, and topsiders while having short hair and no socks.