In organic chemistry, an ethynyl group is a functional group with the formula −C≡CH, representing an acetylene molecule with one fewer hydrogen atom.

• Ethynyl group (HC≡C–), also designated as an acetylenic group (from acetylene), is referred to in IUPAC chemical nomenclature with the -yne suffix. It is sometimes designated as ethinyl in compounds such as ethinylestradiol and ethisterone (ethinyltestosterone). See main page alkynes.