Synonyms for Mg (same or very similar meaning)
WordNet sense 1 (a light silver-white ductile bivalent metallic element; in pure form it burns with brilliant white flame; occurs naturally only in combination (as in magnesite and dolomite and carnallite and spinel and olivine)):
magnesiumWordNet sense 2 (one thousandth (1/1,000) gram):
milligramFrom the ODE community, based on WordNetadd/edit