Heteroclitic

The Proto-Indo-European term *wódr̥ (“water”) is typical of nouns with heteroclitic stems: the strong stem *wódr̥- occurs in the direct cases while the weak stem *wédn̥- is found instead in the oblique cases, hence the contrast between nominative *wódr̥ and genitive *wédn̥s.

[…] a heteroclitic response was never observed after the immunization with the deamidated peptide […]