需 (xū) — to need, to require

需 is a formal/written verb meaning 'to need, to require' — almost always followed by 要 (e.g. 需 + 要). 比 需要 更书面, rarely used alone in speech.

Two or more meaningful parts placed together so that their meanings combine into a new one.

需 originally showed 天, here a person, under 雨, rain, as someone getting wet.