oc·tane (?k?t?n?)n.1. Any of various isomeric alkanes with the formula C8H18, found in petroleum and used as a fuel and solvent.2. An octane number.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.octane (??kte?n) n (Elements & Compounds) a liquid alkane hydrocarbon found in petroleum and existing in 18 isomeric forms, esp the isomer n-octane. Formula: C8H18. See also isooctaneCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014oc?tane (??k te?n) n. any of 18 isomeric saturated hydrocarbons having the formula C8H18, some of which are obtained in the distillation of petroleum. [1870?75;