also: よういドン · よういどん
interjection
ready, go!
Used as a starting signal in races or competitions, equivalent to 'On your marks, get set, go!'.
See also: ドン
先生が「よーいドン！」と叫ぶと、子どもたちは一斉に走り出した。
When the teacher shouted 'Ready, go!', the children all started running at once.
noun
By extension, refers to a race or any contest that starts with this signal; often used metaphorically.
運動会のよーいドンで一等になった。
I won first place in the race at the sports day.
新製品の発売は各社のよーいドンだ。
The launch of the new product is a race among the companies.
All-katakana spelling with long vowel ヨウ; less common than ヨーイドン.
Part of the longer starting command '位置について、用意、ドン' (On your marks, get set, go!). よーいドン is a shortened, casual version.
From the starting command in races: 用意 (yōi, 'get ready') + ドン (don, onomatopoeic for a starting pistol or sudden sound).