Cienna is likely a variant of Sienna, the Italian place-name referring to the city of Siena.
Cienna is usually read as a modern variant of Sienna, the name taken from Siena, the Tuscan city whose name also gave English the pigment term sienna, especially in the familiar phrase "burnt sienna." That gives Cienna an unusual double inheritance: geography and color. The C spelling is newer and more ornamental, but the deeper associations remain Italian.
Through the color word, the name suggests warm earth, painterly richness, and Renaissance atmosphere; through the city, it evokes medieval streets, art, and old stone. Cienna itself is much rarer than Sienna, so its cultural story often runs through the more established spelling. The rise of Sienna in English-speaking countries helped open the door for variant forms like Cienna and Ciena, especially in the late twentieth century when place names and color names began to feel stylish and wearable.
Actress Sienna Miller, along with the general popularity of design-conscious names, helped make the broader name family feel glamorous and modern. Cienna, in turn, offers that same aura with a slightly more individualized edge. The perception of the name has evolved from unusual to legible.
Once it might have seemed like an inventive twist; now it reads as part of a familiar contemporary pattern, though still uncommon enough to stand out. It also benefits from literary and artistic associations rather than direct mythic or biblical ones. Cienna sounds cultured without being formal, visual without being overly whimsical. It is a modern spelling with old-world echoes, and that contrast gives it much of its charm.