The ethynyl group (H -C ≡ C-) - obsolete also ethynyl group - is a functional group in organic chemistry and is an ethyne molecule, from which one hydrogen atom has been removed. The introduction of an ethynyl group in organic chemical compounds by means of acetylides ( Nef reaction ) is called ethynylation. When ethynylation of ketones arise geminal Ethinylalkohole.

The German name acetylenyl is today due to the Anglicisation of the technical language no longer in use and is found only in old descriptions of experiments.