a (mathematics|lay) Having exactly two integral factors: itself and unity (1 in the case of integers).
n (Christianity|historical) One of the daily offices of prayer of the Western Church, associated with the early morning (typically 6 a.m.).
n (fencing) The first defensive position, with the sword hand held at head height, and the tip of the sword at head height.
n (context|algebra|number theory) A prime element of a mathematical structure, particularly a prime number.
n (card games) A four-card hand containing one card of each suit in the game of primero; the opposite of a flush in poker.
v (intransitive|of a steam boiler) To work so that foaming occurs from too violent ebullition, which causes water to become mixed with, and be carried along with, the steam that is formed.