Green’s Dictionary of Slang

1. a crinolette or bustle used for distending the back of a woman’s skirt [it raises or ‘elevates’ the back of the skirt].

1909

J. Ware Passing Eng. of the Victorian Era 123/2: Elevator (Soc., 1882 on). The crinolette. For some years the dress below the back of the waist was almost flat, when in this year bows were seen there, and then followed the crinolette, which, throwing up the dress, obtained this satiric name amongst young men.

2. (UK Und.) a hold-up man, a robber; a shoplifter [pun on SE hold up/hold up v.¹ (1)].

1914		Jackson & Hellyer Vocab. Criminal Sl. 31: elevator [...] In shoplifter’s and holdup men’s parlance. A lifter; a booster; a hoister; – a ‘stick-up’ man.
1926		‘Und. and Its Vernacular’ in Clues mag. 158—62: elevator Holdup man.