1. 1〔すぐに〕
    • 火はたちまち2階に燃え広がった
    • The fire spread to the second floor 「in an instant [instantly/in no time].
    • この薬はたちまち効くということだ
    • This medicine is supposed 「to take immediate effect [to work immediately].
  1. 2〔にわかに〕
    • 口論はたちまち殴り合いに変わった
    • All of a sudden the dispute turned into a fistfight.
    • たちまち大粒の雨が降ってきた
    • It suddenly began to rain heavily.