hyacinth noun [C]. › a pleasant-smelling ​plant with a lot of ​small ​flowers that ​grow ​close together around one ​thick ​stem. (Definition of hyacinth from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press).See all translations.yacinth noun [C]. › a pleasant-smelling ​plant with a lot of ​small ​flowers that ​grow ​close together around one ​thick ​stem. (Definition of hyacinth from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press).