Grit
Noun
すな
小さい頃、あなたとビーチで作った砂のお城を思い出します。
It reminds me of the sand castle that you and I made on beach when we were little.
The kanji and the word are exactly the same. That means they share meanings as well.
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you to remember: If you walk around on the beach, you'll get sand in your shoes sooner (すな) or later.