|Definition - A pronoun — such as each, either, and neither — that references members of a group separately instead of collectively, e.g. To each his own, You can take either of these two courses of action, and Neither of them was happy.|
Oxford English Dictionary - The term's first citation is from 1824:
"The distributive adjective pronouns, each, every, either, agree with the nouns … and verbs, of the singular number only."
(L. Murray Eng. Gram. (ed. 5) I. 247 )