主催
しゅさい · shusai · JLPT N1 · noun
to host
主 — flame/lamp on top of a stand 王
Originally a pictograph of a lamp with a flame on top of its stand, representing the lord or master of the household who tended the fire. The meaning extended from 'lamp/host' to 'master, owner, main, principal'. The character 炷 (wick) preserves the original 'lamp' sense.
催 — person 亻 + 崔 (cuī, phonetic)
催 is a semantic-phonetic compound. The person radical 亻 gives the meaning, since urging or hurrying is something one person does to another, while 崔 supplies the sound 'cui'. The original sense was to press or push someone to act, which broadened to today's meaning of urging, hastening, or prompting.