Pentamethylene \Pen`ta*meth"yl*ene\, n. [Penta- + methylene.]
(Chem.)
A hypothetical hydrocarbon, {C5H10}, metameric with the
amylenes, and the nucleus of a large number of derivatives;
-- so named because regarded as composed of five methylene
residues. Cf. {Trimethylene}, and {Tetramethylene}.
[1913 Webster]