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

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

• Ethynylation
• Ethynyl radical
• Propynyl ( H₃C–C≡C–R, 1-propynyl group; or HC≡C–CH₂–R, 2-propynyl group, Propargyl)