köken: Borrowed in the late 19th century from German Low German klipp und klaar, attested since the 18th century. The adjective klipp, which today occurs only in this idiom, is derived from Middle Low German klippen, itself akin to and roughly synonymous with klappen (“to clap”). It is plausible that it originally referred to the handshake by which a deal is settled.
Ich habe Ihnen eine klipp und klare Anweisung gegeben.