Term for using "thingy-esque" phrases rather than a common word

I absolutely loved this question. Of course, we can all think of a handful of words like thingy, that simply act as a stand-in word for the word we are thinking of but cannot, at present, grasp.

The 1960 Dictionary of American slang uses the term kadigin for placeholder words, defining it as a synonym for thingamajig.

Dr. Richard Nordquist, Professor Emeritus of English, writes in Crossing Boundaries: Studies in English Language, Literature, and Culture in a Global Environment, originally published in 2009:

The linguistic term for such peculiar sounding words as "thingamajig" and "whatchamacallit" is placeholder, or, less formally, tongue-tipper or kadigin: a word used to signal that a speaker does not know or cannot remember a more precise word for something.

William Safire, author, presidential speechwriter, and writer of The New York Time's column "On Language" addresses popular etymology in his incredibly popular, and entertaining, column. The focus of his January 9, 2005 piece, "Whosit's Whatchamacallit" is all about your topic:

"We are now into the creative world of "tongue-tippers," terms used in place of words on the tip of the speaker's tongue but just beyond linguistic reach."

In the article, Safire provides fascinating history and etymology of various tongue-tippers. We also learn that English may not be able to lay claim to all tounge-tippers:

"British English also has its words for the unremembered objects. In 1962, The Sunday Times explained that "'ujah' . . . was used as widely and as indiscriminately as 'gimmick' and 'gadget' are used now." It was usually spelled oojah and was thought to be of Hindustani origin."

I hope you enjoy reading the entirety of Safire's column. Between placeholder, kadigin and tongue-tipper, the last one in my opinion is the best. I think that it's important to have a memorable word when trying to remember the name for the group of words that we use when we just can't seem to remember the actual word.

You seem to be talking about placeholder names

Placeholder names are words that can refer to objects or people whose names are temporarily forgotten, irrelevant, or unknown in the context in which they are being discussed.

Quoting from the wikipedia article:

These placeholders typically function grammatically as nouns and can be used for people (e.g., John Doe, Jane Doe), objects (e.g., widget) or places (e.g., Anytown, USA).

Stuart Berg Flexner and Harold Wentworth's Dictionary of American Slang (1960) uses the term kadigan for placeholder words. They define "kadigan" as a synonym for thingamajig.

Also note:

These words exist in a highly informal register of the English language. In formal speech and writing, words like accessory, paraphernalia, artifact, instrument, or utensil are preferred; these words serve substantially the same function, but differ in connotation.

I know you don't trust wikipedia much, so I'm trying to find other links which use the word:

• 10 PLACEHOLDER NAMES YOU PROBABLY DIDN'T KNOW - Mental Floss

• Placeholder names - Daily Writing Tips

• What Is a Placeholder Name? Wise Geek

I can think of several words that are thingy-type words, like gizmo, widget, gubbins, thingumajig, wotsit, but I don't know of a word for those words. Nonce word is the closest, but to qualify as one of those a word has to be a one-occasion word, invented spontaneously to fill gap that no existing word can fill. The words I listed, as well as thingy itself, are general-purpose fillers that have been used for decades, and I don't think they count as nonce words. There may not actually be a word to describe the category, but no doubt someone will prove otherwise.

In fan discourse, there's the term "Buffy speak," derived from the television series Buffy the Vampire Slayer, which evidently featured a great deal of "thingys" and "whatsits."

More professional sounding phrases would be "forgotten name placeholders," or "approximations."

I believe, while informal, the word "dingus" could be used for a name of something you may not remember. It comes from the Afrikaans word, "ding" for thing.

http://dictionary.reference.com/browse/dingus