taju.

Probably from taitaa + -u, which regularly would give *taitu, but with levelling from the oblique stem (as in i.e. tajuissaan), which in Eastern Finnish sees a regular loss of -d- (thus *taidu- > taju), and with later internal borrowing into the western dialects. Traditionally held to be derived instead from a root *taje- which would have also yielded taitaa, taittaa, taipua, taimi, etc., but the semantic connections are quite weak. For the semantic link between taitaa (in modern Finnish “to know how (to), have mastered”, but more often “may, might”) and taju, note that taitaa has meanings like “to understand” in older language, while taju in some eastern dialects also has the meaning “skill”. Karelian taju is borrowed from Finnish, as are modern Estonian taju, tajuma (< tajuta). The exact nature of taioman olla attested in Wiedemann's Estonian-German dictionary is uncertain, but may also represent a borrowing from Finnish or a parallel derivative.