From the Latin for "measure", it's a small amount of something
[DOC] [TLE] Measure - definition of measure by The Free Dictionary [PAR] [Middle English, from Old French mesure, from Latin mnsra, from mnsus, past 
... 5. a specific or standard amount of something: a measure of grain; short 
measure ..... density of a substance by shining light on it and measuring its 
transmission .... statute, enactment They passed a measure that would give small 
businesses... [DOC] [TLE] Dram - How Many Scruples in a Dram?