Adjective
athematic (not comparable)
(linguistics) Of a root, not having a thematic vowel and thus attaching inflections directly to the root.
In August 1951, just after his first Darmstadt visit, Stockhausen began working with a form of athematic serial composition that rejected the twelve-tone technique of Schoenberg (Felder 1977, 92). Source: Internet
Present indicative The most complex system is the present indicative, consisting of 12 classes, 8 thematic and 4 athematic, with distinct sets of thematic and athematic endings. Source: Internet
The following classes occur in Tocharian B (some are missing in Tocharian A): *I: Athematic without suffix < PIE root athematic. Source: Internet
The other pattern was used by the third, fourth and fifth declensions, and derived from the athematic PIE declension. Source: Internet