Wiktionary
undecanal
n. (context organic compound English) The saturated aliphatic aldehyde having eleven carbon atoms
Wikipedia
Undecanal
Undecanal, also known as undecyl aldehyde, is an organic compound with the chemical formula CHCHO. It is an eleven- carbon aldehyde. A colourless, oily liquid, undecanal is a component of perfumes. Although it occurs naturally in citrus oils, it is produced commercially by hydroformylation of decene.
It has been registered under the EU REACH scheme at >1000 tonnes by Oxea, which confirms the status as irritant.