In mathematics, quadratic means "involving the second and no higher power of an unknown quantity or variable". But the prefix quad- usually describes something that has to do with four, such as quad-core processor and quadrilateral. Why does "quadratic" describe second power when "quad" means "four"?

• Quadratic comes from "quad" meaning square; when you raise something to the second power, you square it. Feb 11 '14 at 11:40
• @NateEldredge ... or, at least in the case of mathematics, quartic. I can't say I've ever actually heard the word "quadric." Feb 11 '14 at 16:18
• @iamnotmaynard: You're right, of course. Brain failure. (Quadric is actually a second-power thing again.) Feb 11 '14 at 16:24

Because the second power is a square, and a square has four sides. In fact the word square itself comes from quad-, too.

• I like the sound of "squaratic equation," come to think of it. Feb 13 '14 at 19:35

Because quadratus is the Latin for "square" due to there being four sides on a square.

The second power of a number is called its square because if we have an integer, and construct a square with that number of items on each side, the total number will be its second power. E.g. a 4×4 square having 16 items:

* * * *
* * * *
* * * *
* * * *

It is also the case that the area of a square with a real number length side, can be measured in terms of the square of that number.

Related language trivia: In the middle of the 16th century, while squared was being used in this sense by some, it had yet to become current, and there was a brief use of zenzic, which means the same thing (via a Latinised, Germanicised, Italian translation from Arabic; it's a convoluted etymology). This form was productive so zenzizenzic meant the 4th power (squared square), zenzicube the 6th (squared cube) and for the 8th power we have zenzizenzizenzic, which is often claimed as the English word with the most Zs in it. It's a doubtful claim though, first there's nothing stopping us from using zenzizenzizenzizenzic to have even more, and second there seems to be about nobody using it any later than 1560 other than in sentences containing the phrase "has the most Zs".

• While the accepted answer got there first, you explain the rationale more clearly. Also, the discussion of zenzic is charming. I once had a math professor who wrote that on the board and asked for speculations on its mathematical meaning. Not one of us guessed it correctly. Feb 11 '14 at 19:52
• All I can think about reading this post is Scrabble. Feb 11 '14 at 20:51
• @emragins you wouldn't be the first, but since there's only one z and two blanks, the word is impossible. Feb 11 '14 at 21:03
• @teylyn added a diagram to the answer to show what I meant. Feb 12 '14 at 0:20
• @teylyn you're adding up the numbers on the four sides of the square. You should be counting the number of spaces in the square (this is equivalent to multiplying the number on one side by itself, which is the same as squaring). You're calculating the perimeter of the square instead of the area. Feb 13 '14 at 18:00