valylene

from The Century Dictionary.

• noun A colorless, oily compound, prepared by the action of alcoholic potassium hydroxid on valerylenedibromide. It has an odor of garlic and boils at 50° C.

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

• noun (Chem.) A volatile liquid hydrocarbon, C5H6, related to ethylene and acetylene, but possessing the property of unsaturation in the third degree. It is the only known member of a distinct series of compounds. It has a garlic odor.

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

• noun organic chemistry The organic compound 2-methylbut-1-en-3-yne HC≡C-C(CH3)=CH2