The kanji 須 generally conveys the meaning of "must," "necessary," "required," or "to be." It implies a need or obligation. It can also suggest something that is essential or indispensable.

・On-yomi (音読み): シュ (shu) ・Kun-yomi (訓読み): すべからく (subekaraku) - This is a more literary reading and means "ought to" or "should."

⚫︎ 必須科目(hissu kamoku) Translation: Required subject; Compulsory subject ⚫︎ 必要(hitsuyou) Translation: Necessity; Need; Essential ⚫︎ 当然の義務(touzen no gimu) Translation: Natural obligation (The kanji 須 is not directly in this phrase, but its concept of "necessary" is related.)

The kanji 須 is a 形声文字 (keisei moji), a phono-semantic compound character. It combines a phonetic component with a semantic component. The phonetic component is a part of another character (possibly 胥, which is now simplified as another character). This component provides the sound. The semantic component is likely related to the idea of the head, implying the head must do something or something is necessary. Over time, the meaning of "must" or "necessary" developed from this.