dram (n.)

mid-15c., "small weight of apothecary's measure," a phonetic spelling, from Anglo-Latin dragma, Old French drame, from Late Latin dragma, from Latin drachma "drachma," from Greek drakhma "measure of weight," also, "silver coin," literally "handful" (of six obols, the least valuable coins in ancient Athens), akin to drassesthai "to grasp" (see drachma). The fluid dram is one-eighth of a fluid ounce, hence "a small drink of liquor" (1713). Hence dram shop (1725), where liquor was sold by the shot.