What is the meaning of whatchamacallit?

Whatchamacallit is a shortened form for What may you call it.

You use whatchamacallit when you are trying to remember the name of something, but you can't.

Example:

Anne: Bob, If you go by the drugstore, please buy one of those...whatchamacallit? The ones I use to swim.

Bob: Oh, you mean year plugs.

Anne: Yes, ear plugs I had totally forgotten the word for it.

Photo credit:

Woman in doubt © Laurin Rinder - Fotolia.com