amyl nitrite

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

• noun A volatile yellow liquid, C₅H₁₁NO₂, formerly used in medicine as a vasodilator, but now replaced by other nitrates, such as nitroglycerin. It is used illicitly to induce euphoria and enhance sexual stimulation.

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

• A yellowish oily volatile liquid, C5H11NO2, used in medicine as a heart stimulant and a vasodilator. The inhalation of its vapor instantly produces flushing of the face.

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

• noun organic chemistry The ester of amyl alcohol and nitrous acid.
• noun informal isoamyl nitrite