blue gum

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

• noun Any of several trees in the genus Eucalyptus of Australia, especially E. globulus, a tall timber tree having smooth bark that peels off in strips and lance-shaped aromatic leaves.

from The Century Dictionary.

• noun In pathology, a blue coloration of the free edge of the gums, frequent in cases of lead-poisoning.
• noun The blue-gum tree.

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

• noun A gum tree of the species Eucalyptus globulus or any of a number of other species of Eucalyptus in Australia.
• noun Australia, Queensland A forest red gum.
• noun slang, offensive A person of sub-Saharan African origin, alluding to the blue coloring around their gumline

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

• noun tall fast-growing timber tree with leaves containing a medicinal oil; young leaves are bluish