必（bì）
Origin:

甲骨文“必”字像一把有长柄的水勺子，旁边有水滴。“必”是“柲”（bì,义为“柄”）的本字，现在多用于指“一定”、“必须”。
On oracle bones inscriptions, “必” looks likes a water spoon with a long handle and water droplets beside it. “必” is the original version of “柲,” and now is more used as “certain” or “must.”

Meaning:

certainly；necessarily；have to；must；

Words：

必须(bìxū): must; have to
必备(bìbèi): essential
必然(bìrán): necessity
必定(bìdìng): to be bound to; be sure to
必不得已(bì bu dé yǐ): to have no choice but
必不可少(bì bu kě shǎo): absolutely necessary

Sentences:

1、Suǒyǒu de gōngzuò míngtiān bìxū wánchéng.
所有的工作明天必须完成。
All the work must be finished tomorrow.

2、Chūmén lǚxíng ，xiàngjī shì bì bù kě shǎo de dōngxi.
出门旅行，相机是必不可少的东西。
The camera is an essential item for travelling.

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