In linguistics, describing a word or verb form that doesn't follow the typical pattern of adding suffixes to a theme or stem (such as irregular verbs).
From a- (without) plus thematic, from Greek thema (theme, subject). The term describes words lacking a clear connecting vowel between root and inflection.
English irregular verbs like 'go/went' are athematic—they don't follow normal rules, which is why English learners find them so frustrating but also why they're usually our most common verbs, since irregular forms survive longest in frequent words.
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