n. a tree of the genus Eucalyptus.
Syn. -- eucalyptus, eucalyptus tree, gum tree. [ WordNet 1.5 ]

n. [ eucalyptus + L. oleum oil. ] (Chem.) A volatile, terpenelike oil (C10H18O), which is the main constituent of the oil of eucalyptus. It has cockroach repellent activity and is used as a flavoring aid in pharmaceuticals. Chemically it is 1, 3, 3-trimethyl-2-oxabicyclo-[ 2, 2, 2 ]-octane. MI11
Syn. -- cineole, cajeputol. [ 1913 Webster +PJC ]

In the 1913 Webster eucalytpol was defined as an oil “consisting largely of cymene”. Cymene (isopropyltoluene, C10H14) differs from that of the substance currently called eucalyptol, in having an unsaturated ring and no oxygen. Para-cymene does occur in eucalyptus oil as well as some other essential oils. [ PJC ]

‖n. [ NL., from Gr. e'y^ well, good + &unr_; covered. The buds of Eucalyptus have a hemispherical or conical covering, which falls off at anthesis. ] (Bot.) A myrtaceous genus of trees, mostly Australian. Many of them grow to an immense height, one or two species exceeding the height even of the California Sequoia.
Syn. -- eucalyptus tree, gum tree, eucalypt. [ 1913 Webster ]

☞ They have rigid, entire leaves with one edge turned toward the zenith. Most of them secrete resinous gums, whence they called gum trees, and their timber is of great value. Eucalyptus Globulus is the blue gum; E. gigantea, the stringy bark: E. amygdalina, the peppermint tree. E. Gunnii, the Tasmanian cider tree, yields a refreshing drink from wounds made in the bark in the spring. Other species yield oils, tars, acids, dyes and tans. It is said that miasmatic valleys in Algeria and Portugal, and a part of the unhealthy Roman Campagna, have been made more salubrious by planting groves of these trees. [ 1913 Webster ]