Real Dictionary

arsenic
uncountable noun: Arsenic is a very strong poison which can kill people.

arsenic in American English
a silvery-white, brittle, very poisonous chemical element, compounds of which are used in making insecticides, glass, medicines, semiconductors, etc.: symbol, As; at. no., 33
of or containing arsenic, esp. pentavalent arsenic
adjective: of or containing arsenic, esp. in the pentavalent state
noun: a grayish-white element having a metallic luster, vaporizing when heated, and forming poisonous compounds; at. wt.: 74.92; at. no.: 33

arsenic in British English
noun: a toxic metalloid element, existing in several allotropic forms, that occurs principally in realgar and orpiment and as the free element. It is used in transistors, lead-based alloys, and high-temperature brasses. Symbol: As; atomic no: 33; atomic wt: 74.