tetrahydrocannabinolPronunciation: /ˌtɛtrəˌhʌɪdrə(ʊ)ˈkanəbɪnɒl, -kəˈnab-/Definition of tetrahydrocannabinol noun [mass noun] Chemistry a crystalline compound that is the main active ingredient of cannabis. Chemical formula: C21H30O2 tetrahydrocannabinol in other Oxford dictionaries Definition of tetrahydrocannabinol in the US English dictionary