spot, n.¹ — Green’s Dictionary of Slang

spot n.¹

[omnibus jargon spot, a plain-clothes official, employed by the company to oversee drivers and conductors; ult. SE spot, to notice]

1. (US) surveillance.

1841

N.Y. Herald 11 Dec. 2/3: John R. Glaize, a large strapping negro, who has been long under the ‘spot’ of the Police, [was arrested].

2. a detective.

1912		cited in Partridge DSUE (1984).
1923		J. Manchon Le Slang.
1933		‘Paul Cain’ Fast One (1936) 49: He was Fenner’s best spot in the Police Department.

3. a guess, a gamble.

1931		D. Runyon ‘The Snatching of Bookie Bob’ in Runyon on Broadway (1954) 127: A spot such as this fifth race with Questionnaire at four to five is like finding money in the street.
1945		A. Christie Sparkling Cyanide (1955) 172: Let’s have your ‘spot.’ You’ve got one, I suppose?

get a spot on (v.)

to make a surveillance of.

1846		N.Y. Herald 14 Jan. 2/5: The hotel keepers would do well to call at the Chief’s office and get a ‘spot’ on the fellow before he is discharged, for no doubt he has been ‘snoozing’ in a number of hotels.
1869		N.Y. Times 19 May 5/1: The modus operandi of ‘testing’ a clerk is as follows: The shadow, after getting a ‘spot’ on the clerk (seeing him for the first time) [...].

put a spot on (v.)

(US black) to focus on, to stare at.

1970

G. Scott-Heron Vulture (1996) 55: John began his question and then put a spot on Debbie over my shoulder, clad only in her slip.