Don’t forget to warm up with some visual training.
All workers are indispensable for Tofugu.
I cannot live without my cell phone.
Remember how 欠ける means "to lack?" Well this is a stronger version because you cuss (かす) at the end. So it means to miss. You're cussing because you aren't just lacking something, you completely missed it: I missed it?! Well $*&%!
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You learned this reading already so you should be able to read it!