I call almost everything a thing-a-ma-jig because my old memory can't remember anything.
Doohickey. Apparently it's a regional word. I have used it in the many places I have lived. Some places people just took the word in stride. Other places I have had people look at me like I have lost my mind.
Doohicky! Yep...... Although truth be told.... It's usually a "that stupid dang blue thing over there!"
That Thing!
I make up a name for it based on what it is. For example, if someone I forgot how to say "faucet" I might say "water bringer."
I once called a cactus a "pokey cabbage" after forgetting the word "cactus."
"The Thing". I'm notorious for it. Drives my kids crazy. That's why I do it.