ultrastructureEnglishOxford New American Dictionaryultrastructure /ˈəltrəˌstrək(t)SHər, ˈəltrəˌstrək(t)ʃər / ▸ noun Biology fine structure, especially within a cell, that can be seen only with the high magnification obtainable with an electron microscope. – DERIVATIVES ultrastructural /ˈəltrəˌstrək(t)SHər(ə)l, ˈəltrəˌstrək(t)ʃər(ə)l / adjective