Irregularly formed or not conforming to standard grammatical patterns.
From Greek hetero- (different) and -klitos (bending/declining), with the Latin adjectival ending -ous, creating a Latinized form of the Greek concept.
This ending in -ous is a tell that we're using a heavily Latinized version of a Greek term, which itself is kind of heteroclitous—a grammatically irregular blending of two language traditions!
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