pentad

UK: /ˈpɛntæd/ US: (pen′tad)

WordReference Random House Unabridged Dictionary of American English © 2026

pen•tad  (pen′tad), n. 

1. a period of five years.
2. Mathematics a group of five.
3. the number five.
4. Chemistry a pentavalent element or group.
5. Meteorology [Climatol.] a period of five consecutive days.

• Greek pentad- (stem of pentás) group of five. See pent-, -ad¹
• 1645–55

Collins Concise English Dictionary © HarperCollins Publishers::

pentad / ˈpɛntæd/ noun

1. a group or series of five
2. the number or sum of five
3. a period of five years
4. a pentavalent element, atom, or radical
5. a period of five days

Etymology: 17th Century: from Greek pentas group of five