1. Any thing, object, piece, part, idea that you cannot remember the name of.
Hoe het it? The thingamajiggers all in a row? Do you mean DNA? Ya!
Synonyms: doohickey, dohingy, thingamabobber, thingamadoo, thingamajig, whatchamacallit.
* This one was inspired by my grandma, who for her frequent lack of a word, often reminds me of the best words I know.