quadratic意為「二次的」，為什麼其前綴是通常與數字4有關的quad?

12-28

二次 ? square ? 方形的 ? 有四條邊。所以有一個拉丁語 4 （quadr-）的詞素。

詞源看 Online Etymology Dictionary

quadratic (adj.)
1650s, "square," with -ic + obsolete quadrate "a square; a group of four things" (late 14c.), from Latin quadratum, noun use of neuter adjective quadratus"square, squared," past participle of quadrare "to square, set in order, complete" (see quadrant). Quadratic equations (1660s) so called because they involve the square of x.
square (n.)
mid-13c., "tool for measuring right angles, carpenter"s square," from Old French esquire "a square, squareness," from Vulgar Latin *exquadra, back-formation from *exquadrare "to square," from Latin ex- "out" (see ex-) + quadrare "make square, set in order, complete," from quadrus "a square" (seequadrant).

可以看出 square 和 quadratic 其實同源，都是 quadrare 演化來的。quad- 前綴如 @Geek.cs 所言，表示有四條邊。

Quad=平方，二次方，你想想square

quadratic:
1.來自 Wikipedia：

In mathematics, the term quadratic describes something that pertains to squares(平方/二次冪), to the operation(運算)of squaring, to terms of the second degree(次/冪), or equations or formulas that involve such terms.
Quadratus is Latin for square.

2.來自iCIBA:

an equation in which the highest power(冪，乘方) of an unknown quantity is a square(平方/二次冪)

二次的意思是指數是2，這樣的東西實際上叫做「平方」。
三次是立方，以這樣的推理，四次是什麼？不知道。因為古人從生活中總結出的數學規律最常見的就是平方和立方。x次冪這樣的是發展出高次冪的問題才開始變得簡便的——唔，我的意思是，二次的這個名字，太間接了。