wolf's-milk

from The Century Dictionary.

• noun A plant of the genus Euphorbia, particularly E. Helioscopia, the sun-spurge. The name is supposed to refer to the acrid milky juice of these plants.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) Any kind of spurge (Euphorbia); -- so called from its acrid milky juice.

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

• noun Any kind of spurge (Euphorbia).

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

• noun tall European perennial naturalized and troublesome as a weed in eastern North America