noun
first person to say something; first person to suggest something; originator of an idea
Refers to the person who first voices an idea, suggestion, or plan in a group. Often used in contexts where someone is reluctant to be the first to speak up.
誰も言い出しべになりたがらなかった。
Nobody wanted to be the first to say something.
彼がその計画の言い出しべだった。
He was the one who first suggested that plan.
発案者 is a more formal term for the person who proposes or originates an idea, often used in business or official contexts. 言い出しべ is colloquial and emphasizes being the first to speak up.
Compound of 言い出し (いいだし, 'starting to say') + べ (a colloquial suffix indicating a person). The suffix べ may be related to 者 (もの, 'person') or a dialectal variant.