Younger Sister, Little Sister
noun
The kanji and the word are exactly the same. That means they share meanings as well.
いもうと
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word: Your younger sister is really into emotes (いもうと). Look up this word if you're not a teenage girl. Just imagine her sending you these on your phone over and over. You tell your younger sister: "HEY, STOP SENDING ME EMOTES."
この子は、私の妹です。
This kid is my little sister.
それは妹のドレスです。
It's my sister's dress.
二人の妹とプールに行きました。
I went to the pool with my two baby sisters.