heteroclite
Irregularly declined or inflected.
Deviating from the ordinary rule; eccentric, abnormal.
dated
he was, on the contrary, as mercurial and sublimated a composition, […] as heteroclite a creature in all his declensions; […] with as much life and whim, and gaité de cœur about him, as the kindliest climate could have engendered and put together.
Where it comes from
From Late Latin heteroclitus, from Ancient Greek ἑτερόκλιτος (heteróklitos), from ἕτερος (héteros, “other, another, different”) + κλίνω (klínō, “lean, incline”), the latter from Proto-Indo-European *ḱley-.
Adapted from the Wiktionary entry heteroclite (CC BY-SA 4.0).