Green’s Dictionary of Slang

1. (also sound out) to elicit information from a person.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 267: sound: to sound a person, means generally to draw from him, in an artful manner, any particulars you want to be acquainted with; as, to sound a kid, porter, &c., is to pump out of him the purport of his errand, the contents of his bundle, or load, &c., that your pall may know how to accost him, in order to draw the swag.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1812].
1859		Hotten Dict. of Modern Sl. etc. 98: sound to pump, or draw information from a person in an artful manner.
1865		Leaves from Diary of Celebrated Burglar 39/2: Nick and I being on very good terms, he continued to ‘sound’ me in regard to this matter of Tommy’s.
1873		Sl. Dict.
1924		G. Henderson Keys to Crookdom 418: Sound. Inquire. Sound him out – to question him.
1951		D. Stivens Jimmy Brockett 162: I’d sounded the Doc and he’d agreed to be chairman of the Olympic Sport Limited.
1958		E. Gilbert Vice Trap 16: Don’t sound me, man.
1967		‘The Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xl 4/4: sound: To sound out, glean information.
1971		E.E. Landy Underground Dict. (1972).

2. to check out, to check over.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 267: To sound a cly, is to touch a person’s pocket gently on the outside, in order to ascertain the nature of its contents.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1812].
1865		Leaves from Diary of Celebrated Burglar 104/1: Joe’s ‘moll’ had by this time ‘sounded’ herself and joined with Jessie in the cry. ‘Why, I’ve lost my gloves, too!’ said she.
1866		H.L. Williams N.-Y. After Dark 91: A friend [...] who slily ‘sounds’ the pockets.
1911		G. Bronson-Howard Enemy to Society 144: I’ll take the chance. ‘Sound’ it! [Ibid.] 189: He would, consequently, have all the time necessary to ‘sound the joint’.
1924		G. Henderson Keys to Crookdom 418: To sound a man – to touch his clothes to locate a purse.
1949		Monteleone Criminal Sl. (rev. edn) 218: sound A pickpocket feeling a victim’s clothes.
1950		Goldin et al. DAUL 201/2: Sound. 1. To search cursorily for concealed weapons or contraband by patting the pocket surfaces. 2. (Pickpockets) To pat the pockets of a prospective victim to locate concealed valuables.
1980		J.L. Gwaltney Drylongso 225: These doctors could see what was happening, you know, but they didn’t want to sound this bitch in front of me.

3. fig., to work something out, to ascertain.

1926		Wood & Goddard Dict. Amer. Sl.
1960		‘Lord Buckley’ Hiparama of the Classics 15: Soundin’ whether this Nation or any other Up There Nation [...] can stay With It, All The Way!

4. to knock on a door to see if the occupants are at home.

1933		C.E. Leach On Top of the Und. in DSUE (1984).
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 10: Sound: Knock at the door of a house to see if anyone is in before breaking in.

5. (US black/teen, also sound on) to inform, to tell.

1942		Pittsburgh Courier (PA) 22 Aug. 7/7: Sound me — (let me know).
1955		Babs Gonzales ‘The Be-Bop Santa Claus’ 🎵 As he eased in close and sounded on Pops.
1960		E. De Roo Big Rumble 28: You guys elect me president to sound or be sounded for?
1975		E. Torres Carlito’s Way 129: ‘So don’t be sounding me about what you is or you ain’t gonna do’.
1982		W.D. Myers Won’t Know Till I Get There 71: ‘[D]on’t come sounding no garbage to me because I don’t want to hear it’.

6. (street gang) a synonym/replacement for dozens n. (1); to tease, to taunt, to joke with (in a ritualized manner).

1962		R.D. Abrahams ‘Playing the Dozens’ in Jnl Amer. Folklore July-Sept. 209: The dozens are commonly called ‘playing’ or ‘sounding,’ [2] and the nature of the terms indicates the kind of procedure involved; ‘playing’ illustrates that a game or contest is being waged, and ‘sounding’ shows that the game is vocal [...] [2] This is the more common way of referring to the game today. "Dozens" is not even understood by some Negroes now.
1969		T. Kochman ‘“Rapping” in the Black Ghetto’Trans-action Feb. 32/2: Sounding is the term which is today most widely known for the game of verbal insult known in the past as ‘Playing the Dozens,’ ‘the Dirty Dozens’ or just ‘the Dozens’.
1972		W. Labov Lang. in the Inner City 306: The term sounding is by far the most common in New York and is reported as the favored term in Philadelphia [...] Sounding is also used to include such insults and includes personal insults of a simpler form. Somebody can ‘sound on’ somebody else by referring to a ritualized attribute of that person.
1994		(con. 1940s–50s) C. Major Juba to Jive.
2021		J. Ellroy Widespread Panic 121: ‘Don’t sound me, muchacho’.

7. to listen, to hear.

1958

High School Confidential [film script] Talk up man, I don’t sound you at all.

8. to insert some form of rod (solid or hollow) into the urethra for sexual pleasure.

2014		M. McBride ‘Sounding’ in ThugLit Mar. [ebook] I used to work with a guy named Jim who liked to stick things in his peehole. They call it ’sounding’.
2018		Metro (London) 3 Jan. 🌐 Generally an activity for the more experienced sexual adventurer, sounding is the act of sliding a (very well lubricated) rod down the urethra – the bit of your anatomy that you pee out of – for pleasure.