Crystal
noun
A water crystal is just a crystal. I guess crystals are clear and look kind of like water, yeah? That's why it's being referred to as a water crystal, making it really just a crystal.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
この水晶は大中小の三つの大きさがあります。
This crystal comes in three sizes; small, medium, and large.
An update is needed before you can continue but you have more than one WaniKani tab open.
Finish up what ever you are doing on the other tab(s), then close them to continue.
The update will complete automatically once the other tab(s) are closed.