lupulin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A yellowish-brown substance obtained from glands at the base of the strobili of the hop plant, containing essential oils and formerly used in medicine as a sedative.

from The Century Dictionary.

• noun The peculiar bitter aromatic principle of the hop. Also called lupulite.
• noun An alkaloid found in hops.
• noun The fine yellow powder of hops, which contains the bitter principle.
• noun Also humulin, humuline.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A bitter principle extracted from hops.
• noun The fine yellow resinous powder found upon the strobiles or fruit of hops, and containing this bitter principle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany Small hairs gotten from the strobili of the hop plant.