Dopamine (DA, contracted from 3,4-dihydroxyphenethylamine) is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the brain and body.
The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave (or other periodic event) for an observer moving relative to its source.
In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical properties.
There have been allegations of doping in the Tour de France since the race began in 1903. Early Tour riders consumed alcohol and used ether, among other substances, as a means of dulling the pain of competing in endurance cycling.
A doppelgänger or doppelga(e)nger (/ˈdɒpəlˌɡɛŋə/ or /-ˌɡæŋə/; German: [ˈdɔpəlˌɡɛŋɐ], literally "double-goer") is a look-alike or double of a living person, sometimes portrayed as a paranormal phenomenon, and is usually seen as a harbinger of bad luck.