See quotation.

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1847.  [Many years ago, in what were frontier settlements, it was customary in stage-coaches for passengers to make room by putting their knees between those of their opposites; and this was called dove-tailing. A Lake captain once sat opposite a fat old lady, and, finding the accommodation scanty, said:] “I guess, marm, it’s got to be done anyhow sooner or later, so you and I, marm, must jist ‘dovetail.’” The lady bounded from her seat, aghast at the mysterious proposal. “Must what, sir—r?” “Dovetail, marm; you and I have got to dovetail, and no two ways about it.” “Dovetail me, you inhuman savage!” she roared out, shaking her fist in the face of the skipper, who shrank, alarmed, into his corner; “dovetail a lone woman in a Christian country! If thar’s law on airth, sir-r, and in the State of Illinoy, I’ll have you hanged!”—G. F. Ruxton, ‘Adventures in Mexico,’ p. 328–9.

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