Ask HN: Where did Webster look up the definitions when he wrote the dictionary?

I can't answer that question.

But I think a more interesting question is: How did James Murray, the original editor of the OED, go about crafting the definitions that went into his dictionary?

For the answer I recommend that you read Caught in the Web of Words by Murray's granddaughter, K. M. Elisabeth Murray.

In a network that in some ways anticipated the free software movement, Murray mailed books to volunteers in English-speaking countries around the world, asking them to document salient occurrences of words they found in the texts they received. The scraps of paper returned to Murray in Oxford filled cubbyholes in "The Scriptorium," a special addition to Murray's house.

As a Christian with a interest in scholarship, I love Murray's motto: "Have thy tools ready; God will find thee work."