To Lack Something
transitive 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 lack, and this verb simply means to lack something.
It's a transitive verb. That means that it takes a direct object. You lack something. Like a car, concentration, or a soul. This is different from 欠ける, which happens all by itself.
かく
You learned this reading when you learned 欠ける, but here's a mnemonic just in case:
You never know when you're going to lack something. Like a car (か). Did you plan for it to break? NO! But it happened and now you lack a car in a big way. Not cool (く)!
工事の音が、集中力を欠く原因だ。
The reason you lack concentration are those construction noises.
バナナだけの食事はバランスを欠いていると思いますよ。
I think your banana-only diet lacks balance.
インターネットは私たちの生活に欠くことのできないサービスだ。
The internet is an indispensable service in our lives.