To Get Fat, To Gain Weight, To Grow Fat, To Become Fat
intransitive verb, godan verb
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means fat so the verb form of that is to get fat.
ふとる
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You have to learn the ふと portion of this word to be able to read it. Here'a mnemonic to help you: It's easy to get fat if you're always in your futon (ふと).
ジュースばっかりのむと太るよ。
You'll get fat if you only drink juice.
たべても太らない人がうらやましい。
I envy people who don't get fat even though they eat a lot.
さいきん犬が太ってきたので、いっしょにダイエットをしてます。
As my dog is gaining weight these days, we are on a diet together.