To Get Sacked
Expression and Godan verb
くびになる
先月、会社を首になりました。
I was fired from the company last month.
しゅう金したお金をつかいこんだら、首になるに決まってるじゃん！
Of course you would get fired, if you used up the collected money.
マーチングバンドを職場に引き連れてきたことが理由で、私は昨日首になりました。
I got sacked yesterday for bringing a marching band into work with me.
The になる part means "to become," so literally this means "to become neck." If you think about it, when something becomes neck, it has to do with you getting your head cut off (at the neck). But, in today's modern society we don't do that too often. Instead, this means you lose your job, aka to get fired.
This word contains the reading you learned with the kanji. Everything else is hiragana.