Head over to Archive.org. Borrow Volume I (A-B). And spend an afternoon falling in love with the history of human speech.
Many illegal websites claim to offer the OED as a free, downloadable PDF. They often contain malware, OCR errors that scramble the text, or missing pages.
But here is the catch: A full, physical print set of the OED costs thousands of dollars and takes up an entire shelf. A digital subscription requires a hefty annual fee or a library card.