A peasant in Monty Python and the Holy Grail complains about the monarchy and how "supreme executive power should come from a mandate from the masses." His name is Dennis. In the musical version, Spamalot, this peasant is Dennis Galahad, who later becomes a very attractive knight.
My brother's name is Dennis. I think it makes him seem both strong and gentle. He weathered the whole Dennis the Menace thing, being that he was born like a year before the character debuted. But, you know what, people make the names they are given not the other way around and when I hear the name Dennis, I don't think of that dumb kid in the comics and tv show, I think of a Highland warrior or an English Lord or something. A funny aside -- my brother Dennis was a phenomenal tennis player in his youth! Ok. That got him ribbed a bit!
Dyns (pronounced: DIN-is), with its Welsh root name, Ynys (pronounced: IN-is) is a feminine form for Dennis. Also, Diynys, with alternate spellings like, Dee-Ynys (pronounced: dee-IN-is), functions well as a feminization of Dennis, too. If you are looking for a Welsh girl's name and you favor the boy's name Dennis, consider the first and middle name combination of, Dynys Enlli, as Ynys Enlli is a Welsh place name of an island considered to be the fabled Isle of Avalon from Authurian legend.
I don't really like most names that end in the 's' sound, and the masculine ones are even worse than the feminine ones, except for maybe Mavis, which is even worse than this name, for instance. Besides, I never did like Dennis the Menace, and that's what comes to mind, as does the occasional American pronunciation of 'dentist'. Gah, not a great association that one, either.
A famous bearer is American actor Dennis Franz (born October 28, 1944). He is best known for his role as Andy Sipowicz in the television series "NYPD Blue", for which he won 4 Emmy Awards.