zona pellucida /ˌzəʊnə pɪˈluːsɪdə 
/ ▸ noun (plural zonae pellucidae /ˌzəʊniː pɪˈluːsɪdiː/) Anatomy Zoology the thick transparent membrane surrounding a mammalian ovum before implantation. – ORIGIN mid 19th century: from Latin, literally ‘pellucid girdle’.
EnglishOxford Dictionary of English
