The Collaborative International Dictionary
tetrahydrocannabinol \tet`ra*hy`dro*can*nab"i*nol\
(t[e^]t`r[.a]*h[imac]`dr[-o]*k[a^]n*n[a^]b"[i^]n[add]l), n.
(Chem. & Med.)
A chemical substance ( C21H20O2) which is produced by the
hemp plant (Cannabis sativa), and is the physiologically
active agent of dried preparations of that plant, called
variously marijuana, hashish, ganja, hemp, etc.; also called
THC. It causes the euphoric effect for which the
preparations are smoked or chewed. It is used in medicine in
a purified form as an antiemetic (an antinausea agent),
especially in conjunction with chemotherapy of cancer. It
occurs primarily as the [Delta]1-3,4-trans isomer, also
called [Delta]9-THC, with small amounts of the
[Delta]6-3,4-trans isomer detectable at about 1%. It is a
controlled substance, classified as a hallucinogen, and its
possession and distribution is illegal in almost all states
of the United States.
--MI11