This word is derived from thing-a-ma-jigger or thing-a-ma-bob as a shorter term. Is the appropriate word to use when you forget the name of somthing or a word you were going to say.
Although it is often used for nouns with adjectives so that the other person can understand what the item maybe.
-Person 1- "may i have uh, you know, um, that, uh, that thingy thing, you know, um, the one, on the table, by the pepper..."
-Person 2- "you mean the salt?"
-Person 1- "Yeah! that's it!"
When you have to recall, or explain something and don't rly remember it's name, or it's not on the top of your head , so you refer to it as a"thingy majigy".