Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
doubleheader is a noun meaning "two games instead of one (especially in baseball when the same two teams play two games on the same day)". It carries one recorded sense.
two games instead of one (especially in baseball when the same two teams play two games on the same day)
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 doubleheader come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.