osteoblast Syllabification: (os·te·o·blast)Pronunciation: /ˈästēəˌblast/Definition of osteoblast noun Physiology a cell that secretes the matrix for bone formation. Derivatives osteoblasticPronunciation: /ˌästēəˈblastik/ adjective osteoblast in other Oxford dictionaries Definition of osteoblast in the British & World English dictionary