How to sign: the 3rd letter of the Roman alphabet
Categories: alphabetic character, letter, letter of the alphabet
How to sign: the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second
Similiar / Same: speed of light, light speed
Categories: constant, speed, velocity
How to sign: an abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds
Similiar / Same: carbon
Categories: chemical element, element
Within this category: activated carbon, carbon black, char, charcoal, diamond, fullerene, graphite, radiocarbon