microgramn.

1890 New Sydenham Soc. Lexicon Microgramme, a measure of weight..it is equivalent to the one thousandth of a milligramme.

1904 Science 30 Sept. 443/1 The figures represent the number of micrograms (= 0.001 milligram) in 100 grams of substance; that is, parts per million.

1930 Proc. Royal Soc. B. 106 544 The quantity of lysin (usually measured in microgrammes).

1940 Industr. & Engin. Chem. (Analyt. ed.) 15 June 359/2 The Committee on Nomenclature, Spelling, and Pronunciation of the American Chemical Society has approved the following recommendation of the Division of Microchemistry: For 0.001 milligram the term ‘microgram’, designated by the symbol γ (the word ‘gamma’ should not be used as a substitute for ‘microgram’).

1953 R. W. Fairbrother Text-bk. Bacteriol. (ed. 7) vii. 80 Streptomycin..is supplied in powder form and the official unit is equivalent to one microgramme (0.001 milligramme) of pure streptomycin base.

1964 New Scientist 24 Sept. 793/1 Dr. Bertrand Goldschmidt..managed to obtain, on an ‘old boy basis’, about 3 microgrammes of plutonium.

1996 Ecology 77 2423 All pupae and 20 larvae were dried and the mass determined to the nearest microgram.