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 FutureKing.
Claire- "Hey, Adam, hand me the- the- you know, the whachamacallit."
Confusion about the understanding of the word whachamacallit. This genious added the special K to the word to say that the word is "killer"
Derailed thoughts keep this on the tip of his tounge.
It like "thingy for Dummies.
Whatkamacallit is Vokabulry for the genious to confuse and derail his friends from getting deep in his mind.