also: せーの · せいの · セイノー · いっせいの · いっせーの
ready, set, go!; all together now!; heave-ho!
Interjection used to coordinate a simultaneous group action, like lifting a heavy object or starting a race. The exact English equivalent depends on context.
On 'ready, set, go,' let's lift it together.
みんなでせーの！
All together now!
Variant spelling; irregular kana usage.
Extended form with いっ; used in some regions or for emphasis.
Extended form with いっせい; irregular kana usage.
Katakana spelling with a long final vowel; may appear in manga or casual writing.
The origin is uncertain. It may derive from 一斉に (いっせいに, 'all at once') or a contraction of それ (sore) and えい (ei), but there is no consensus.