dell n.1

level or gently sloping ground between low hills with a stream flowing through it, Old English dæl "vale, valley, gorge," from Proto-Germanic *dalaz "valley" (source also of Old Saxon, Dutch, Gothic dal, Old Norse dalr, Old High German tal, German Tal "valley"), perhaps from PIE *dhel- "a hollow" (source also of Old Church Slavonic dolu "pit," Russian dolu "valley"), or perhaps a substratum word. It was preserved by Norse influence in the north of England. Related: Dalesman.

"rogue's girlfriend, beggar's mistress," 1520s, slang, of unknown origin (see dell (n.2)). Liberman says it is probably from Low German dokke "doll," "with the deterioration of meaning from 'sweetheart' and 'wench' to 'whore.'"