Oaks are a group of trees and shrubs from the Northern hemisphere. There are both deciduous and evergreen oaks. Most people are familiar with the common oak trees that grow acorns.
Oak wood is used for making furniture, and was once used for making houses. It is still used for making winebarrels.
An oar, sometimes called a paddle, is a long, thin pole with a wide, flat part at one or both ends. It is used to make a small boat like a canoe move forward, and to help in steering it.
Oats are a cereal crop grown mainly for turning into rolled oats and oatmeal for making porridge. It is also used as animal feed, particularly for horses.
An obelisk is a 3 dimensional shape with four sides, tapering towards the top. Obelisks are usually tipped with a pyramid. They are a popular shape for monuments.
Oboes are a double reed musical instrument in the woodwind family. Oboes have a very clear sound, and can be heard over other instruments. They have a conical hole through their centre, unlike the flute which has a cylindrical one.
An observatory is a building that is made as a place to watch the stars and planets. Observatories are dome-shaped and are usually built on top of high mountains so there is less air between them and space.
Obsidian is a dark glass formed in the larval flows of volcanos. Obsidian doesn't have a crystalline structure and can be broken into very thin pieces that can be used to make a very sharp cutting edge, spear tip or arrow head.
An obtuse angle is one that is larger than 90 degrees. A 90 degree angle is a "normal" corner, like you find inside most houses and the corners of a piece of paper. An angle smaller than 90 degrees is called acute.
