The term 'PORTENTOUS DECK' is a crossword solution that refers to the Tarot, a type of card deck used for divination and fortune-telling. The Tarot is composed of 78 cards divided into two sections: the Major Arcana, which consists of 22 cards, and the Minor Arcana, which consists of 56 cards. The Major Arcana cards are often seen as having greater significance than the Minor Arcana cards, and are said to represent the spiritual journey of the individual.