a tall fast-growing widely cultivated Australian myrtaceous tree, Eucalyptus globulus, having aromatic leaves containing a medicinal oil, bark that peels off in shreds, and hard timber. The juvenile leaves are bluish in colour
2.
any of several other eucalyptus trees
See also red gum (sense 1)
blue gum in American English
a large evergreen tree (Eucalyptus globulus) of the myrtle family, native to Australia, having smooth, deciduous bark and aromatic leaves: grown extensively in California