Green’s Dictionary of Slang

1. the mouth.

1825		J. Neal Brother Jonathan I 143: Shet your clam.
1833		J. Neal Down-Easters I 93: Shet your clam!—like that better?—hold your yop!
1917		R. Lardner ‘The Water Cure’ Gullible’s Travels 172: I kept my clam closed and tried to be pleasant.
1920		R. Lardner Big Town 180: I’m going to tell you a secret and if you don’t keep your clam shut I’ll roll you for a natural.
1950		Goldin et al. DAUL 44/2: Clam. [...] 2. The mouth.
1957		H. Simmons Corner Boy 200: You better open your clams and talk.
2001		S. King Dreamcatcher 451: Close your clam, you son of a bitch.

2. (US, also clamshell) the vagina, the hymen; thus, by metonymy, a woman (see cit. 2005).

1842		Wkly Rake (NY) 27 Aug. n.p.: the rake wants to know What tall Sarah was doing with that cab driver in a vacant oyster celler in Bleecker street [...] if she was showing him how to open oysters or clams .
1855		Broadway Belle, and Mirror of the Times (NY) 12 Mar. 6/4: [He] asked [a young lady] if she had been eating clam soup. ‘No,’ she replied, ‘I have got clam enough.’.
1865		‘Philocomus’ Love Feast vi. 52: He shoved his tool her / little clam in.
1894		Mirror of Life 17 Mar. 15/1: [US speaker] ‘Jack, y' done a good thing when y’ shook that skinny clam y' uster travel with’.
1902		D. St John Memoirs of Madge Buford 116: Ah, your cock it is a beauty. / Put it slam — in my clam.
1925		E. Field ‘A French Crisis’ in Facetiae Americana 20: Or with his facile penis clave a virgin’s clam in two.
1929		Bessie Smith ‘Kitchen Man’ 🎵 Oh how that boy can open clams / [...] / I can’t do without my kitchen man.
1938		‘Justinian’ Americana Sexualis 16: Clam [...] the maidenhead. Generally refers to a hymen which is difficult to pierce.
1974		(con. 1960s) R. Price Wanderers 105: She’d probably scrub her clam so damn clean it would win a Good Housekeeping award.
1975		Manchester Guardian Weekly 2 Aug. 20: Bette Midler is [...] no Streisand, her material is blue and her songs are old. Yet she’s been camped out at one of Broadway’s biggest theatres for several months now, making raunch respectable in a sellout revue called Clams on the Half Shell.
1994		G. Indiana Rent Boy 60: Mavis groans and whispers [...] ‘Ahhh, yeah, fuck it, fuck it, fuck that clam.’.
2000		M. Manning Get Your Cock Out 45: One fell between young Dandy’s legs and started chowing down on her sanctified clam.
2005		J. Stahl I, Fatty 153: The clams Mack hired showed a lot of thigh and smoked like steam trains.
2023		R. Milward Man-Eating Typewriter 139: ‘She’s a randy beggar [...] been known to offer her clamshell after dark’.

3. (US) a fool, a worthless individual.

1866		‘Mark Twain’ ‘Travelling Show’ in Screamers (1875) 150: That lets you out, you know, you chowder-headed old clam!
1889		‘Mark Twain’ Connecticut Yankee xii 155: These innumerable clams had permitted it so long that they had come [...] to accept it as a truth.
1889		Kipling ‘Shadow of His Hand’ in Civil & Military Gaz. 2 Aug. (1909) 39: ‘Loan him money then and settle him on the other side of the States,’ I used to say. ‘The old clam won't move’ .
1896		W.C. Gore Student Sl. in Cohen (1997) 10: clam. n. [...] 2. A stupid person.
1898		F. Dumont Dumont’s Joke Book 42: Jays are called ‘clams’.
1905		Minneapolis Jrnl (MN) 12 Nov. 5/2: Don’t be a clam, my son.
1923		M. Garahan Stiffs 216: And when we’re both in jail it will be you, you clam, who [...].
1924		G. Henderson Keys to Crookdom 400: Clam. A victim, a sucker, gull, sap, boob.
1931		O. Strange Law O’ The Lariat 60: ‘Bloomin’ clam,’ he muttered disgustedly.
1949		Wodehouse Mating Season 81: Poor deluded clam.

4. (also clamface, clam-mouth) a tight-lipped person.

1896		W.C. Gore Student Sl. in Cohen (1997) 10: clam. n. 1. A very reticent person.
1909		W.M. Raine Brand Blotters (1912) 165: ‘Shut up!’ ordered the man [...] ‘I’m a clam,’ retorted the other.
1912		Van Loan ‘McCluskey’s Prodigal’ Ten-Thousand-Dollar Arm 271: ‘Keep your trap shut.’ [...] ‘Like a clam! They’ll get nothing out of me.’.
1920		F. Packard White Moll 167: ‘Aw, open up!’ she snapped. ‘Wot’s de use bein’ a clam! [...] Where is he?’.
1936		W.R. Burnett King Cole 6: ‘[H]e’s not the Read Cole he used to be. He’s a clam. No telling which way he’ll jump’.
1944		C. Himes ‘Money Don’t Spend in the Stir’ Coll. Stories (1990) 194: I closed up. Call me clam-mouth, brother, I said; call me oyster.
1949		I. Shulman Cry Tough! 130: I’m a clam.
1955		B. Appel Tough Guy [ebook] Here was a guy who once’d given out with the words like they each cost a quarter. A regular clam face.
2002		X-Files Season 8 Episode 3 ‘Redrum’ 🌐 Doggett: His name is Cesar Ocampo. He’s got a full sheet…assault and narcotics. He knows the drill. He’s a clam.

5. (US) a mean person; thus tight as a clamshell, very close-fisted.

1902

Ade Forty Modern Fables 9: Permit your Affections to Center on some Tractable Person who is neither a Prospective Pauper nor a close-fisted Clam.

6. an untrustworthy person.

1915

M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 197: clam, sneaking fellow. ‘He’s a regular clam.’.

7. (US) in pl., the hands.

1969		in DARE.
2002		D.H. Sterry Chicken (2003) 65: I’m not looking, but my clams are getting sweaty.

8. (US) a Scientologist [note American Dialect Society List 10/5/99: ‘I remember reading an explanation of the term years ago, but have forgotten the specifics. It goes *something* like this: in L. Ron Hubbard’s sci-fi religion, souls of alien refugees (who were hiding in volcanoes on Earth) were released when their enemies dropped atom bombs on them. These souls came to reside in clams (and early humans?)’].

1999

ADS-L 10 May : Someone wrote that the shooters were ‘clams’ (Scientologists). There were 1400 hits for ‘clam’/‘Scientologist’ on the Usenet database.