The boy’s eyes […] ran over Spade’s body from shoulders to knees, […] ¶ “Another thing,” Spade repeated, glaring at the boy: “Keep that gunsel away from me while you’re making up your mind. I’ll kill him. […] ”
(street and prison slang) A passive partner in anal intercourse.
By misunderstanding of the 1929 Maltese Falcon quotation above (which survived in a popular 1941 film adaptation). The novel was originally serialized in a magazine, Black Mask, whose editor refused to allow vulgarities. Hammett used the word gunsel knowing that the editor would likely misunderstand it as relating to gun, and therefore allow it.
^William Safire, “Dirigiste” (On Language column, 2000 April 30), in The New York Times; relevant portion also in The Right Word in the Right Place at the Right Time, Simon and Schuster (2004), →ISBN, page 35.
^Michael Quinion, “Gunsel” (World Wide Words piece, 2006 August 12).