Old-fashioned, mostly seen in costume drama and rural-novel contexts where deals (land sales, marriage matches) needed a trusted third party to witness and mediate. Modern equivalents:
中介 (zhōngjiè, broker/agency),
介绍人 (jièshàorén, introducer). Don't confuse with
中年人 (zhōngniánrén, "middle-aged person") — the missing
年 changes the meaning entirely.
