A word used when the actual name of the object in question will not come to mind. Very versatile but often very vague. It is derived from the phrase "what-you-may-call-it" which can be found in T. H. White's The Once and Future King.
Claire- "Hey, Adam, hand me the- the- you know, the whatchamacallit."
An awesome candy bar, very, very sexified. Peanutbutter... Caramel... chocolate.... mmmmmm.
Also, its that thing that you can never remember the name for.
1. Mmmmmm, whatchamacallit
2. GAH! whats that thing... you know, the whatchamacallit?