Of first importance.
prime minister the head of an elected government; the principal minister of a sovereign or state. In Britain Robert Walpole is regarded as having been the first Prime Minister in the modern sense. By the middle of the 19th century the term had become common in informal use, and in 1905 it was formally recognized.
prime number a number that is divisible only by itself and unity (e.g. 2, 3, 5, 7, 11). Formerly also, the golden number.