Mencken, H.L. 1921. Columbia Encyclopedia World Factbook Columbia Gazetteer American Heritage Coll. The American Language.
Most etymologists derive the word from the Dutch doop, a sauce.
In English, as in American, it signifies a thick liquid, and hence the viscous cooked opium. Hop is simply the common name of the Humulus lupulus. The belief that hops have a soporific effect is very ancient, and hop-pillows were brought to America by the first English colonists. The derivation of poker, which came into American from California in the days of the gold rush, has puzzled etymologists. It is commonly derived from primero, the name of a somewhat similar game, popular in England in the sixteenth century, but the relation seems rather fanciful.