noun, noun which may take the genitive case particle 'no', na-adjective
A somewhat formal or literary term for a pressing situation requiring immediate action. Often used in official or written contexts.
火急の用事で、すぐに帰らなければならなかった。
I had to go home immediately due to an urgent matter.
この問題は火急を要する。
This problem requires urgent attention.
緊急 is the common, everyday word for 'emergency' or 'urgency'. 火急 is more formal and less frequent, often used in written or official language.
The exact derivation is uncertain; the kanji 火 (fire) and 急 (urgent) combine to suggest a pressing, fire-like urgency.