1.
to be fired; to be dismissed from one's job
To lose one's job; literally 'to become a neck', from the image of a beheading. Colloquial; the transitive 首にする means to fire someone. In casual writing the word is often クビ in katakana.
Literally 'to become a neck': the neck is what gets cut. Colloquial; in writing the word is often クビ.
Common patterns
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Casual and blunt. Formal announcements use 解雇 (dismissal).