1807, American English, "sauce, gravy, thick liquid," from Dutch doop "thick dipping sauce," from doopen "to dip" (cf. dip (v.)). Extension to "drug" is 1889, from practice of smoking semi-liquid opium preparation. Meaning "foolish, stupid person" is older (1851) and may have a sense of "thick-headed." Sense of "inside information" (1901) may come from knowing before the race which horse had been drugged to influence performance. Dope-fiend is attested from 1896.
1889, from dope (n.). Related: Doped; doping.
A narcotic, especially an addictive narcotic.
An illicit drug, especially marijuana.
To explain or clarify; figure out: I doped that all out myself (1906+)
[fr Dutch doop, ''sauce for dipping,'' with elaborate semantic shifts]