An octagon is an 8 sided 2 dimensional shape. A cylinder with the base of a hexagon (6 sided shape) would be an 8 sided 3 dimensional shape.
A 14-sided and 3-dimensional shape is called either a tetrakaidecahedron or tetradecahedron. This 14-sided polyhedron can have six quadrilateral and eight hexagonal faces.
A 3 dimensional triangle is called a pyramid, otherwise a 2D three sided polygon shape is exactly what you called it, a triangle.
A 10-sided shape is known as a decagon.(A decahedron is a 3-dimensional solid with 10 polygonal faces.)
A scalene triangle.
Octahedron
a polyhedron (if the shape is 3 dimensional) a polygon if it is a planar shape.
An 18 sided shape is called a octadecagon. This refers to both 2 dimensional and 3 dimensional shapes in a mathematical sense.
A triangle is a 3 sided shape. There are a few types, Isosceles, Scalene (Acute and Obtuse), Equilateral and the Right angle triangle.
A 5-sided 2-dimensional figure is a pentagon and a 5-sided 3-dimensional shape is a pentahedron.
An octagon is an 8 sided 2 dimensional shape. A cylinder with the base of a hexagon (6 sided shape) would be an 8 sided 3 dimensional shape.
A 12 sided figure is called a dodecagon. A 3-dimensional shape with 12 faces is called a dodecahedron.
If a polygon (2 dimensional shape) then it is a 2000-gon. If a polyhedron (3 dimensional solid), then it is a 2000-hedron.
If it's a 2-dimensional shape, like lines drawn on paper, a 12 sided shape is called a dodecagon. If it's 3-dimensional, like a 12-sided die, then it's called a dodecahedron.dodecagon
A 14-sided and 3-dimensional shape is called either a tetrakaidecahedron or tetradecahedron. This 14-sided polyhedron can have six quadrilateral and eight hexagonal faces.
A pyramid
In geometry a 29 sided shape is referred to as an icosikaidigon. The shape closely resembles an 3 dimensional octagon.