一斉

1. Origins, structure, and basic meaning

• Structure: The spelling is 一斉, read いっせい, and it combines 一, meaning one or together, with 斉, meaning aligned or simultaneous.
• Basic usage: The basic sense of 一斉 is multiple people or things acting or changing together at the same cue or time.

2. Common pitfalls and similar expressions

• Many movements beginning together
  • Both examples use the form 一斉, appearing as 一斉に to modify an action. The focus is coordinated timing among multiple entities, not the speed of one action.
• A starting signal and spring blooming
  • 合図とともに選手たちが一斉に走り出した。 — At the signal, the athletes all started running at once.
  • 春になると庭の花が一斉に咲く。 — The flowers in the garden bloom all at once in spring.