Variant of Denise, feminine of Dennis, from Greek Dionysos, god of wine and revelry.
Dennise is an uncommon variant spelling of Denise, the French feminine form of Denis, which in turn descends from the Latin Dionysius — itself the Latinization of the Greek Dionysus, the god of wine, theater, and revelry. That mythological root gives the name a heritage of creative vitality and pleasurable excess that its refined French surface keeps politely in check. The path from Olympian deity to everyday given name took roughly two millennia and passed through the martyrdom of Saint Denis, the first bishop of Paris, who was beheaded around 250 AD and became the patron saint of France.
Denise entered the English-speaking world through French influence and flourished through the mid-twentieth century, particularly in the 1950s, 60s, and 70s in the United States, Canada, and Britain. Notable bearers include Denise Richards, the American actress, and Denise Lewis, the British heptathlete who won gold at the 2000 Sydney Olympics — two very different women whose shared name nonetheless suggests range and capability. In French culture, Denise carries a more everyday, working-class warmth, associated with the kind of competent, no-nonsense Parisian woman who keeps things running.
The Dennise spelling, with its doubled 'n', is rarer and functions as a personalizing variant — the kind of orthographic choice that was especially popular in mid-century American families who wanted a familiar name with a slightly individual stamp. It doesn't alter the pronunciation but gives the name a visual distinctiveness on paper. Today Dennise occupies vintage territory: retro enough to feel unexpected on a young child, but substantial enough that it carries no whimsy or trend-chasing. It is a name with provenance.