Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
inion is a noun meaning "the craniometric point that is the most prominent point at the back of the head (at the occipital protuberance)". It carries one recorded sense.
the craniometric point that is the most prominent point at the back of the head (at the occipital protuberance)
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for inion come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.