What are Three-ing words?

There's no recognized term called "Three-ing words". It's possible you're thinking of a word that sounds similar or has a related meaning, but it's not a common linguistic term.

Could you please clarify what you mean by "Three-ing words"? For example:

* Are you thinking of a specific word that you can't quite remember? If so, give me some clues about the word, like the first letter, or what it might relate to.

* Are you thinking of a type of word? Maybe you're thinking of words with a specific number of syllables, or words that have a particular function in a sentence.

Let me know, and I'll do my best to help!