What the prefix for cup?

There isn't a specific prefix for "cup" in the way there might be for other words like "bicycle" (bi-) or "triangle" (tri-).

However, you might encounter words related to cups like:

* Teacup: This uses "tea" as a prefix, though it isn't a true prefix in the linguistic sense.

* Coffee cup: This uses "coffee" as a prefix, similar to "teacup."

If you're thinking about a specific concept, let me know, and I can help you find the right word.