I find that I know most of the words which thefreedictionary.com publishes in its Word of the Day. Today's word, tenebrous, was no exception. It means dark and gloomy. What caught my eye was the word listed as the synonym: tenebrific. Now that's a word I've never seen before. So I checked the definition: thefreedictionary says it means dark and gloomy. Well, I guess that's to be expected, since it was listed as a synonym to a word that means exactly that. Not completely satisfied, I went to dictionary.com, where I got a significantly different definition: producing darkness. I like that. That I can use. But I'm not so sure people will understand what definition I want when the dictionaries say different things (I will point out that another source, which gives the definition as "dark and gloomy," then goes on to use tenebrous, rather than tenebrific, in their example sentence, but I think the source is more thesaurus than dictionary).
Ah, well. I still like the word, and I hope someday to make the "producing darkness" definition the accepted one.