"flak". Merriam-Webster Online Dictionary. Diarsipkan dari versi asli tanggal 14 May 2008. Diakses tanggal 30 June 2008.
oed.com
"ack-ack, adj. and n.".Error in webarchive template: Check |url= value. Empty. OED Online. September 2013. Oxford University Press. (accessed 14 September 2013).