Green’s Dictionary of Slang

dell n.

also del, dill
[poss. SE name Doll or, in the way that cunt n. is linked to Welsh cwm, a valley, then a pun on SE dell, also meaning valley; Ribton-Turner, A History of Vagrants (1887), notes Welsh del, pert, smart; Lowland Scot. dilp, a trollop]

1. [mid-16C–early 19C] a young woman on the tramp, spec. a young or ‘unbroken’ (i.e. virgin) prostitute; thus wild dell, such a young woman conceived or born under a hedge.

2. [late 18C] a prostitute.

In phrases

arch-dell (n.)

[early 18C–mid-19C] (UK Und.) the woman accomplice of a criminal gang-leader (cf. doxy n.).