Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
amastia is a noun meaning "absence of the mammary glands (either through surgery or developmental defect)". It carries one recorded sense.
absence of the mammary glands (either through surgery or developmental defect)
surgery
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 amastia come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.