General need:
* 必要 (hitsuyou): This is the most common and versatile word for "need." It implies a general requirement or necessity.
* 要る (iru): This word means "to need" and is used when talking about a specific thing or action.
For specific types of need:
* 必要性 (hitsuyou-sei): This word refers to the "necessity" or "importance" of something.
* 要望 (youbou): This word means "request" or "demand," and can be used to express a need for something specific.
* 欠ける (kakeru): This word means "to be lacking" or "to be deficient," and can be used to express a need for something that is missing.
* 欲しい (hoshii): This word means "want" or "desire" and can be used to express a personal need or want.
Examples:
* 私は新しい車が必要です。 (Watashi wa atarashii kuruma ga hitsuyou desu.) - I need a new car.
* この仕事には経験が必要です。 (Kono shigoto ni wa keiken ga hitsuyou desu.) - This job requires experience.
* 私は新しい本が欲しいです。 (Watashi wa atarashii hon ga hoshii desu.) - I want a new book.
The best word to use will depend on the specific situation and what you are trying to express.