I hate when my husband twists the caps back on plastic bottles really tightly.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means closed so the verb vocab version is to close.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You need to close the door or the sheep (し) will come in. Not just one sheep, or two, but hundreds of sheep. They'll see you didn't manage to shut that door properly, and when you turn around your house will be covered floor to ceiling with fat squishy sheep.