Definition of pentynyl in US English:

pentynyl

(also pentinyl)

noun

Chemistry
rare
  • An unsaturated hydrocarbon radical with the formula —C₅H₇; (now) specifically one containing a carbon–carbon triple bond. Usually as a formative element in chemical names.

Origin

Late 19th century; earliest use found in Henry Forster Morley (b. 1855). From pentyne + -yl.