informant; survey respondent
Borrowed from English 'informant'. Often used in academic or research contexts for a person who provides information, especially in surveys or linguistic fieldwork.
In this survey, we interviewed 50 informants.
言語学のフィールドワークでは、現地のインフォーマントの協力が不可欠だ。
In linguistic fieldwork, the cooperation of local informants is essential.