The process, state, or condition of having or possessing a tail or tail-like structures.
From caudate (having a tail) plus the noun-forming suffix -ion, creating an abstract noun describing the quality or state of being tailed or having tail-like features.
This word is so specialized that even most biologists probably don't use it—it's the kind of ultra-technical term that exists in dictionaries but sounds almost like scientists are just playing with Latin suffixes.
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