The Collaborative International Dictionary of English v.0.48:

Drachm \Drachm\, n. [See Drachma.]
   1. A drachma.
      [1913 Webster]

   2. Same as Dram.
      [1913 Webster]

WordNet (r) 3.0 (2006):

drachm
    n 1: a unit of apothecary weight equal to an eighth of an ounce
         or to 60 grains [syn: dram, drachm, drachma]
    2: a British imperial capacity measure (liquid or dry) equal to
       60 minims or 3.5516 cubic centimeters [syn: fluidram,
       fluid dram, fluid drachm, drachm]
    3: a unit of capacity or volume in the apothecary system equal
       to one eighth of a fluid ounce [syn: fluidram, fluid
       dram, fluid drachm, drachm]