Whatsit

There are many placeholders used in English. These are words added to a sentence to replace the correct noun, usually due to the speaker not being able to think of the word immediately, or perhaps thinking that the noun (thing, person) is not worth actually mentioning.

Whatsit, thingummy, what’s-his-name, so-and-so, oojamaflip, doohickey

Examples:

• Whatsit: “Can you pass me that whatsit over there? You know, the little plastic tool for opening the battery cover.”
• Thingummy: “I need to go to the hardware store to get a new thingummy for the kitchen tap; it’s started leaking again.” (Note: In British English, you might also hear thingummyjig or thingummybob).
• What’s-his-name: “I ran into what’s-his-name at the supermarket—the guy who used to live in the blue house at the end of our street.”
• So-and-so: “I don’t want to be a gossip, but I heard that so-and-so from the accounting department is planning to quit on Monday.”

That last one, so-and-so, is also used as a general term to describe somebody who is not nice or troublesome:

That new guy is a right so-and-so!