changing location rapidly | a piece of calcite or a similar substance, usually in the shape of a crayon, that is used to write or draw on blackboards or other flat surfaces |
a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression | an amphetamine derivative (trade name Methedrine) used in the form of a crystalline hydrochloride; used as a stimulant to the nervous system and as an appetite suppressant |
a rate (usually rapid) at which something happens | a pure flat white with little reflectance |
the ratio of the focal length to the diameter of a (camera) lens system | a soft whitish calcite |
distance travelled per unit time | |