Numeral prefix

Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example:

• triangle, quadrilateral, pentagon, hexagon, octagon (shape with 3 sides, 4 sides, 5 sides, 6 sides, 8 sides)
• simplex, duplex (communication in only 1 direction at a time, in 2 directions simultaneously)
• unicycle, bicycle, tricycle (vehicle with 1 wheel, 2 wheels, 3 wheels)
• dyad, triad, tetrad (2 parts, 3 parts, 4 parts)
• twins, triplets, quadruplets (multiple birth of 2 children, 3 children, 4 children)
• biped, quadruped, hexapod (animal with 2 feet, 4 feet, 6 feet)
• September, October, November, December (7th month, 8th month, 9th month, 10th month)^[A]
• binary, ternary, octal, decimal, hexadecimal (numbers expressed in base 2, base 3, base 8, base 10, base 16)
• septuagenarian, octogenarian (a person 70–79 years old, 80–89 years old)
• centipede, millipede, myriapod (subgroups of arthropods with numerous feet, suggesting but not implying approximately 100, 1000, and 10000 feet respectively)

In many European languages there are two principal systems, taken from Latin and Greek, each with several subsystems; in addition, Sanskrit occupies a marginal position.^[B] There is also an international set of metric prefixes, which are used in the world's standard measurement system.
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