Q From Imelda Anwar, Singapore: What is the meaning of dealybob? Where did the word originate?
A This puzzled me, too, since I’d never come across the word. An online search suggested that it could be one of those hand-waving words for a nameless small object or something whose name for the moment one can’t remember, perhaps a thingummy or thingamajig, a whatsisname, or a doohickey (“Put this dealybob on the end of a hose, feed it into the drain pipe and turn on the water”). I’ve also found it used for some unclassifiable event or activity (“Data goes on a long, pointless Method Acting dealybob in this last-season episode”). It seems to be originally and mainly American.
As so often, it’s hard to find out where it comes from, though it’s plausibly suggested that it derives from deal. Several slang senses in American English are based on its meaning of a business agreement or transaction. One of them is some unspecified action or turn of events, as in expressions like what’s the deal?, which can mean “what’s going on?”. By the 1940s deal could refer to any unspecified thing or person. The next step was to put -y on the end to turn it into a sort of diminutive, and then -bob was added as a meaningless flourish or ornament, presumably from one or other of the expressions that contain it, like the now outmoded thingumbob. So Americans ended up with dealybob.
The first part of the word seems to have been borrowed for two US trade names, although in a slightly different spelling. In the 1960s a deelybobber was a type of construction toy. In the 1980s the same name (though often spelled deelybopper) was applied to that daft headwear that consisted of two balls on flexible antennae attached to a band. Though both words are in the OED, neither is listed in any American dictionary, most probably because their periods of fashion were too short-lived to register in any dictionary that takes a snapshot of the current state of the language.