interjection
Casual, often dismissive or perfunctory acknowledgment. Can sound like a half-hearted 'yeah, yeah'.
「ちゃんと宿題やった？」「へいへい、やったよ。」
"Did you do your homework properly?" "Yeah, yeah, I did."
adverb, noun or participle which takes 'suru'
sycophantically; servilely; fawningly
Describes an obsequious, overly agreeable manner. Often used with verbs like 言う or 返事する.
彼は上司にへいへいと従っている。
He obsequiously follows his boss's orders.