Green’s Dictionary of Slang

dancer n.

1. [mid-18C+] a cat burglar who ‘dances’ along the roof and in through a convenient window, or a thief entering a house to rob the upstairs, when the residents are not in bed, or are out; thus usu. a daylight robbery; 20C use also refers to those who steal from empty offices [SE dance, later strengthened by dance v. (3)].

2. [mid-19C] one who copulates [dance v. (1)].