The O.E.D. is a historical dictionary, providing citations meant to show the evolution of every word, beginning with the earliest known usage. So a key task, and a popular sport for thousands of volunteer word aficionados, is antedating: finding earlier citations than those already known. This used to be painstakingly slow and chancy. When Paton started in new words, she found herself struggling with headcase. She had current citations, but she says she felt sure it must be older, and books were of little use. She wandered around the office muttering headcase, headcase, headcase...
See here. [NYTimes]