Bile was a bitter yellow liquid, secreted by the liver that aided in absorption and digestion.
In 2151, Jonathan Archer told Phlox that Humans used to collect the bile of black bears to be used as an aphrodisiac. (ENT: "Fight or Flight")
In 2365, on the tenth anniversary of Worf's Rite of Ascension, he intoned as part of the ritual: "The bile of the vanquished flows over my hands." (TNG: "The Icarus Factor")