Poly-
A closed plane figure with many straight lines that connect
Polygon
An eyeglass for one eye
Monocle
A writer
Journalist
A three sided figure
Triangle
Having two different colors
Bicolor
A person who knows how to speak, read, or write many languages
Polyglot
A track for subway or train cars that only has one rail
Monorail
A person who see the positive side of things
Optimist
A vehicle with three wheels
Tricycle
A two footed creature
Biped
Having many different colors
Polychromatic
A speech in which every word has one tone of voice
Monotone
A person who takes care of teeth
Dentist
Three related plays or novels
Trilogy
Happening every two weeks
Biweekly
A lie detector test
Polygraph
Having one color
Monochrome
An expert in a certain field
Specialist
Able to speak 3 languages
Trilingual
Eyeglasses with lenses that have two different sections
Bifocals
Belief in many gods
Polytheism
Control of a product or service by one company
Monopoly
A person who loves and tries to protect nature
Naturalist
A race that combines 3 activities
Triathlon
Happening every two years
Biennial