Regnant is an adjective that means dominant or widespread.

Coming from the Latin word regnare (ren YAR ay) which means ‘to reign,’ - R-E-I-G-N - our word of the day can mean anything that is dominant, either because it is forced upon people, as in from a reigning king or queen, or simply because it is popular. Here’s an example of the latter: I thought my clothes in high school were what the cool kids wore, but I soon realized that it had been years since my plaid shirts and checkered sweaters were the regnant style.