primordium
Concise Oxford English Dictionary © 2008 Oxford University Press:
primordium /prʌɪˈmɔːdɪəm/
▶noun (pl. primordia /-dɪə/) Biology an organ, structure, or tissue in the earliest stage of development.
– origin C19: from L., neut. of primordius.
'primordium' also found in these Oxford entries:

