a canal for a current of water | changing location rapidly |
a contest of speed | a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression |
any competition | a rate (usually rapid) at which something happens |
people who are believed to belong to the same genetic stock | the ratio of the focal length to the diameter of a (camera) lens system |
(biology) a taxonomic group that is a division of a species; usually arises as a consequence of geographical isolation within a species | distance travelled per unit time |
the flow of air that is driven backwards by an aircraft propeller | |