The story
Originally a trademark, suggested by the wife of product marketer John Minkove; it had been her schoolfriend's placeholder name for an unspecified object (thus perhaps from dealie).
Etymology from Wiktionary, CC BY-SA 4.0.
deely bobber
Today it means: A novelty headband, popular in the 1980s, with two springy antenna-like protrusions topped with small pompoms or other ornaments. Full definition →