↑ Simpson, John biên tập (2009). Oxford English Dictionary, 2nd edition, on CD-ROM Version 4.0. Oxford: Oxford University Press. ISBN978-0-19-956383-8.
↑ Stevenson, Angus; Lindberg, Christine A. biên tập (2010). New Oxford American Dictionary, Third Edition. New York: Oxford University Press. tr. 300. ISBN978-0-19-539288-3.
