The bitter exudate from the castor sacs of mature beavers(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "castoreum" in a sentence
"The scent is leathery and animalic think both indolic and uric at once, and with that dry leathery undertone – hence it is most commonly described as a cross between civet and castoreum, which is a pretty good description if you ask me."
"It was not, however, till of late years that the sagacious Indians discovered that the castoreum was a certain bait for the animals themselves."
"They are seen near these dams and at their "lodges" on the banks of the stream, where they ooze out this castoreum, which is understood to be a signal to other beavers."