nitrogen mustard

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of a group of toxic organic compounds that are structurally similar to mustard gas but contain nitrogen instead of sulfur, used primarily as chemotherapeutic agents.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry any of a series of compounds, analagous to mustard gas with sulfur replaced by nitrogen, that have been used in the treatment of cancer

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a toxic compound resembling mustard gas in structure; important in cancer treatment