Ergo, you need more than one resource. Linguist David Crystal boasts that he refers to more than 100 dictionaries. That’s perhaps a touch OCD but at the other end, one is too few.
Wajnryb compared three dictionaries and found that each had a different thought to contribute in order to attain a fuller meaning. The answer to the question of how many dictionaries, seems to be more than one but less than 100, no doubt depending on context and circumstance.