To Tighten
To Tie, To Wrap Up
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, like a screw, or to tie, like a necktie or towel.
締める can also mean to wrap up when used in reference to a speech or some other occasion. In Japanese culture, people often 締める a situation with some shared action, like clapping in rhythm to end a celebration or having a final bowl of ramen to close out a night. You call it 締める because it's like you're tying off the event and giving it a sense of closure.
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?
どんな言葉で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!