primordium
noun
pri·mor·di·um prī-ˈmȯr-dē-əm 
plural primordia prī-ˈmȯr-dē-ə
: the rudiment or commencement of a part or organ
Example Sentences
Recent Examples on the Web Sun spells out a half-century of empirical research, along with the roles of complex genetic signals, hormones, chromosomes and a small group of cells called the bipotential primordium. 
Heidi Stevens, chicagotribune.com, 26 Feb. 2021
Heidi Stevens, chicagotribune.com, 26 Feb. 2021 Word History
Etymology
borrowed from German Primordium, borrowed from Latin prīmōrdium (in plural prīmōrdia) "beginnings, origin, source, elementary stage" — more at primordial
First Known Use
1855, in the meaning defined above
Medical Definition
primordium
noun
pri·mor·di·um -ē-əm
plural primordia -ē-ə
: the rudiment or commencement of a part or organ : anlage
the gonadal primordium