The ability to speak eloquently and at length/knowledgeably

Years ago, I had read, and then looked up the word for this, but I have since forgotten it, cannot find it, and not being able to recall this word has driven me crazy since.

It's a rarely used or seen word that describes a person who has the ability to, or maybe it was an adjective for just the quailty of ones' speech to be eloquent, spoken with ease and at length and knowledgeably, or at least perceived as knowledgeable/educated on any given topic, via the quality of their speech.

The "at length" part I think was key to include since the word meant more than just being articulate or eloquent in general, it also described the ability to convey a depth of knowledge, whether truly possessed or not.

Something like "the author had the ability to speak _____-ly, and enrapture the audience," or, "the author was _____, able to keep the crowd utterly captivated"

Kind of like a verbosity, but in a good/convincing/skillful way.

It's not a compound word or phrase. It's not / I've searched the thesauruses for erudite / eloquent / articulate / well-spoken / persuasive / verbose / compelling / impassioned / insightful / perspicacious / trenchant... none of them really hit it on the head.

(I think the word was in a Grantland or TheRinger article, FWIT...) Maybe I'm mistakenly conflating the content of the article with another memory of some other word, I sure hope not.

Thanks for any thoughts!

We can all provide examples of words we think fit the meaning requested, but this is an impossible question because there is no way any of us can know the exact word you read in an article years ago.

There is no word I know which captures both concepts simultaneously, and, if there is one, it is probably too esoteric to be useful. I would argue that eloquent itself is a good word for the examples provided. If you feel that it does not sufficiently convey the point that the speaker is knowledgeable, you simply may need to use more than one word to ensure that your audience appreciates the nuance of your point.