Meaning

noun a vibrating device that substitutes for an erect penis to provide vaginal stimulation

originRelated to other nonsense syllables like dido and diddle(-diddle), which similarly developed sexual senses. Found since at least the 1500s, often in contexts where allusion is being made to the sexual sense (above). Possibly influenced by Middle English dildoun (“darling, pet”), early modern English dildin (“sweetheart”); compare Old Norse dilla (“to lull”), dillindo (“lullaby”).

Etymology from Wiktionary, CC BY-SA 3.0