Interesting words: doohickey
when you see something that you don’t know the name of, and probably don’t even know the function of, you can call it a doohickey.
For example, “I’ve finished assembling this IKEA wardrobe, but what on earth am I supposed to do with this doohickey?”
Another similar word is “thingumabob” or “thingamajig”. British have shortened those words to “thingy”.