To Tighten
To Tie
transitive verb, ichidan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means tighten so the verb vocab version means to tighten.
You go to tighten and to tie your captive up, and you realize you don't have anything to do it with. Then you see a sheep standing nearby. Okay. You take the sheep (し), pull its wool, and tie the sheep and your captive up together around a tree. Problem solved!
ガスの元栓、ちゃんと締めた？
Did you tightly turn off the gas?
どんな言葉をスピーチを締めるべきか迷っているんだ。
I'm wondering what words would be good to wrap up the speech.
ちょっと待って。シートベルト、まだ締めてない！
Wait a minute. I haven't fastened my seatbelt yet!
ネクタイの締め方は分からないけど、ネジを締めるのは任せて！
I don't know how to put on a tie, but leave it to me to tighten the screws!