3. Acute: is derived from the Latin word acus for needle, with derivatives for that referring to anything sharp or pointy. An acute angle is one that is sharp or pointy.
4. Angle: comes from the Latin root angulus, which is a sharp bend. Ankle comes from the same root.
5. Algebra: comes from an Arabic book that revolutionized how mathematics worked in western cultures. The first word in the book "Al-jebr w'al-mugabalah" became the word Algebra in western languages.
6. Geometry: derived from the conjuction of the Greek word for Earth, Goes, and the term for "to measure", metros.
7. Hypotenuse: comes from the Greek root hypo (for under), and tein (for stretch). The hypotenuse was the line segment "stretched under" the right angle.
8. Multiply: Combines the roots of multi, many, and pli, for folds, as in a number folded on itself many times. Multiply seems to have been first used by Chaucer in "A Treatise on the Astrolabe".
9. Quadratic: is the Latin root for "to make square".
10. Secant: is from the Latin root Secare, meaning to cut. It is a name for the segment that cuts through a circle. The word was introduced by Thomas Fincke in 1583.
11. Subtract: is a conjuction of two roots, sub (under or below) and tract (meaning to pull or carry away).
12. Square: is derived from the Latin phrase Exquadrare, later contracted into its present meaning of the regular quadrilateral.
13. Tangent: Is from the Latin root tangere, meaning to touch, describing two curves which meet at a single point. Tangent is a creation of Thomas Fincke, written by him around 1583.
14. Zero: comes from the Arabic word "sifre".
15. Symmetry: is a conjunction of sum and metros. The prefix refers to things which are alike.
16. Sequence: is from the Latin root sequi, meaning "to follow". In mathematics, it refers to a series of terms in order, so a pattern between numbers.
17. Plus: comes from the early latin word meaning "more".This word is closely related to the Greek root "poly" (many).
18. Negative numbers: the word for negative was introduced by Brahmagupta, a Hindu mathematician around 600 A.D. The Latin root of today's word is negare, meaning "to deny".
19. Obtuse: is from the Latin formation ob(against) and tundere(to beat). An object, when beaten, becomes blunt, dull, or rounded, and the application to an obtuse angle is in this sense.
20. Fraction: comes from the Latin word frangere, meaning "to break". A fraction represents a broken whole, in this sense.
