|Word root/ prefix||Root Meaning||Words based on the Root|
|Numer||Number||Enumerate - to mention a number of items on a list
Numerology - the study of magical uses of numbers
Numerous - a large number.
|Oct/a/o||eight||Octagon - a figure with 8 sides and 8 angles
Octogenarian - person in his or her 80s
Octopus - sea animal with 8 arms.
|Omni||all||Omnipotent - with all the power
Omniscient - knowing all things
Omnivorous - eating all foods.
|Opt||best||Optimal - the best, the most desirable
Optimize - to make the best of
Optimum - the best something could be
|Ortho||straight||Orthodontist - a dentist that straightens teeth
Orthopedic - a doctor concerned with the proper alignment of the bones
Orthography - the correct way of writing.