The plural is anomymous (eg Alcoholics Anonymous).The plural of the word in the original greek would be something like anonym-οι or anonym-oi in the latin alphabet.The dipthong oi in greek is pronouced usually like "oi" in the "oil however in some case(this being one of them) is pronounced like "e"in "email".What I dont get is how the word ended up to be anonymous rather than anonymus since words like colossus have the same suffix in greek.