You're right to ask! There aren't many common science words that start with "Y". Here are a few, depending on the specific field:

General Science:

* Yield: This is a common term in chemistry and physics, referring to the amount of product obtained from a reaction or process.

* Yttrium: A chemical element with the symbol Y.

Biology:

* Yolk: The nutrient-rich part of an egg.

* Yeast: A type of fungus that is crucial in baking and brewing.

Geology:

* Yellowstone: A famous volcanic caldera in the United States.

* Yellow sand: A type of sand that is often found in deserts.

Other:

* Young's modulus: A measure of a material's stiffness in physics.

Let me know if you'd like more examples or would like to explore words from a specific scientific field!