long-chain fatty acid monounsaturated fatty acid octadecenoic acid Any member of the group of C18 monounsaturated fatty acids with the double bond located at any position in the chain. C18H34O2 CHEBI:25634 PMID:18832207 PMID:19106329 PMID:7276754 chebi_ontology octadecenoic acid olefinic fatty acid