So I caught this article from a recent fan post by jonmark93, and Demarius Thomas was asked about the meaning of his name. His mom told him that he'd be the only one with that name, and that was about all he could really state for certain about the meaning of his name. Well, I certainly can't speak to the intentions of a parent in naming their kid something as unique as Demarius Thomas, but being an English major I have a certain interest in language, so I decided to break it down a little bit.
My first thought on really looking at the name was that I recognized Marius. On top of being an English major, I was also a French minor, and a huge part of the reason I decided to learn French was Victor Hugo's Les Miserables, in which a major character is names Marius. Marius was somewhat of a heroic figure, so when I saw Marius in Demarius' name, I felt a bell chiming in my head. French is largely derived from Latin, so it's not a stretch to think Marius might have meaning in Latin, and "De" is also a Latin/French word (it's like "the", "a", "of").
From what I can tell, the most well-considered origin of the name Marius is that it is derived from Mars, the god of war. So you could take Demarius to mean "of war" or "having to do with war", or perhaps "warrior." The other couple of meanings I saw that were considered possibilities were "Male" and "sea". So you could imagine a manly sea of war rolling down the field, knocking opposing cornerbacks out of position to snag a ball and run it in for a touchdown. Obviously, all of this is playful supposition and isn't meant to take anything away from the personal nature of his name.
However, I, for one, can't wait to see our man-warrior crushing opponents backfields. GO BRONCOS!!!