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EnchantedLearning.com Math Dictionary

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O is for ...

obelisk An obelisk is a tall, four-sided tower topped with a pyramid.

oblique Lines or planes are oblique when they are neither parallel nor perpendicular to each other.

obtuse angle An obtuse angle is an angle greater than ninety degrees.

obtuse triangle One of the interior angles of an obtuse triangle is obtuse ( an obtuse angle is over 90 degrees).

octadecagon An octadecagon is an eighteen-sided figure.

octagon An octagon is an eight-sided figure. Stop signs are octagons.

octahedron An octahedron is an eight-sided geometric solid (a 3-D object).

1, 3, 5, 7, 9, 11, ... odd number An odd number is not divisible evenly by two.

one One is the number between zero and two. One is the multiplicative identity, since one times any number is equal to that number.

1/2 one half When something is divided into two equal parts, each of these two parts is one half of the original object.

operation An operation is a rule for taking one or two numbers as inputs and producing a number as an output. Some arithmetic operations are multiplication, division, addition, and subtraction.

opposites Opposites are things that are very, very different from each other. Some examples of opposites are: positive and negative, add and subtract, left and right, big and small, up and down.

orb An orb is a ball-shaped object.

order of magnitude The order of magnitude is the estimate of size (or magnitude) expressed as a power of ten. For example, a 100 ft (102 ft) tall building one order of magnitude taller than a 10 ft (101 ft) tall building.

order of operations In mathematical operations, the standard order of operations is: Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction. Within a category, operations are done from left to right.

ordinal number Ordinal numbers show order. Some ordinals are first (1st), second (2nd), third (3rd), fourth (4th), fifth (5th), sixth (6th), seventh (7th), eighth (8th), ninth (9th), tenth (10th), eleventh (11th), twelfth (12th), etc.

ordinate Ordinate is another name for numbers on the y-axis (the vertical axis). The ordinate is the second number in a point (x,y).

origin The origin is the point (0,0) -- where the x and y axes meet. In a 3-d coordinate system, the origin is the point (0,0,0) -- where the x, y and z axes meet.

ounce An ounce is a unit of measure. Eight ounces are one cup.

oval An oval is an egg-shaped figure.

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EnchantedLearning.com Math Dictionary

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Counting

Addition

Subtraction

Multiplication

Division

Number Line

Fractions

Decimals

Graphs

Measurement

Rounding

Click on an underlined word for more information on that subject. If the math term you are looking for is not in the dictionary, please e-mail us.

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