Several parts combine into one character.

急 originated as a compound ideograph showing 及 (jí, "to reach / to overtake — a hand reaching to grab a person") on top, with 心 (heart) on the bottom. The composite picture is visceral: a hand approaching to seize you, your heart constricting in response = urgency, haste. The top component evolved into the current shape over centuries but the original tension of the etymology remains palpable. Few characters convey their semantic charge as physically as 急.

Korean reading "geup." Pervasive across medical, transport, and financial vocabulary: 急行 (geuphaeng, express train / express service), 急性 (geupseong, acute — medical), 緊急 (gingeup, emergency / urgent), 應急 (eunggeup, first aid / emergency response), 急騰 (geupdeung, "sudden surge" = sharp rise — used in stock market reporting), 急減 (geupgam, sharp decrease). The Korean (eunggeupsil, "emergency room") is the standard hospital ER.

Mandarin jí, 2nd tone. 急 (jí, urgent / impatient), 着急 (zháojí, "stuck in urgency" = anxious / worried — high-frequency emotional vocabulary in spoken Chinese: 别着急 bié zháojí = "don't worry"), 紧急 (jǐnjí, urgent), 急忙 (jímáng, in a hurry), 急救 (jíjiù, "urgent rescue" = first aid / emergency rescue). 急 also functions as a description of personality: 性子急 (xìngzi jí) = "having an impatient temperament."

Japanese on-reading キュウ (kyū) — 急行 (kyūkō, express train), 急性 (kyūsei, acute illness), 緊急 (kinkyū, emergency — extremely common in safety announcements and news), 救急車 (kyūkyūsha, "rescue-emergency vehicle" = ambulance — note the doubled キュウ sound), 急患 (kyūkan, emergency patient). Kun-reading いそぐ (isogu, to hurry) — 急ぐ (isogu), 急いで (isoide, "hurry up" — common command), 急に (kyū ni, "suddenly" — note this uses the on-reading キュウ unusually as an adverbial form). 急に雨が降った (kyū ni ame ga futta, "suddenly it started raining") demonstrates the kyū-ni adverb pattern that's essential to Japanese conversation.

Memory aid: a hand reaching to grab (top) above a constricting heart (心) — the body's response to urgency, encoded as a character.