You can't say "the first English word" just like that. What English? Old English? Anglo-Saxon? Germanic-influenced... English has adopted thousands of words from other languages over the ages (still does). Another point to consider: Languages (no matter which ones) have been given from father to son, from mother to daughter, orally. Reading and writing made their path to England centuries later.
If you're really interested in this field, I can recommend you read "Mother Tongue" by Bill Bryson. It's a very interesting read, I'm enjoying it immensely!