Brenna is of uncertain origin; it is usually explained as a feminine form of the Irish surname Brennan or as derived from the Irish bran, "raven", and it is often grouped with Brenda. It has a Celtic lilt without the heavy spelling that many Irish names carry. Brenna ranked number 310 in 2000, peaked at number 296 in 2003 and has fallen steadily since, from number 792 in 2015 to number 1846 in 2025.