Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
equinoctial is an adjective and noun meaning "relating to the vicinity of the equator". It carries 3 recorded senses.
relating to the vicinity of the equator
relating to an equinox (when the lengths of night and day are equal)
the great circle on the celestial sphere midway between the celestial poles
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 equinoctial come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.