athematic Syllabification: (a·the·mat·ic)Pronunciation: /ˌāTHiˈmatik/Definition of athematic adjective 1 Music (of a composition) not based on the use of themes. 2 Grammar (of a verb form) having a suffix attached to the stem without a connecting (thematic) vowel. athematic in other Oxford dictionaries Definition of athematic in the British & World English dictionary