Meaning:

certainly；necessarily；have to；must；

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.”

Words:

   必不可少 (bì bu kě shǎo): absolutely necessary

   必不得已 (bì bu dé yǐ): to have no choice but

   必定       (bìdìng): to be bound to; be sure to

   必然      (bìrán): necessity

   必备      (bìbèi): essential

   必须     (bìxū): must; have to

Examples:

1. 出门旅行，相机是必不可少的东西。

    Chūmén lǚxíng ，xiàngjī shì bì bù kě shǎo de dōngxi

    The camera is an essential item for travelling.

2. 所有的工作明天必须完成。

    Suǒyǒu de gōngzuò míngtiān bìxū wánchéng

    All the work must be finished tomorrow.