adjective/a.te.ma.tik/
athematic (said of a formation in which the suffix is attached directly to the root, without the help of a thematic morpheme)
“Au présent athématique ancien sont souvent substitués d'autres types, variables suivant les langues[…]” — The ancient athematic present tense is often replaced by other types, which vary according to the language […]
Related: athématisme
From a- + thématique.