is everyone single or plural
It is an adjective that serves to modify nouns. Nouns modified by every are singular and must be written in such a manner. For example: Every <person> involved in the crash died. The reason for this singularity is because the word every literally means each, and refers to a single entity. Moreover, another reason for this is every is derived from the terms everything and everyone.. Notice here that obviously thing and one are singular objects.