Latin word postea comes from Latin ea, Latin post

Detailed word origin of postea

Dictionary entry	Language	Definition
ea	Latin (lat)	On that side. That way. There Accusative neuter plural of is: "them (things)". Nominative feminine singular of is: "she", "it" (referring to feminine nouns). Nominative neuter plural of is: "they (things)".
post	Latin (lat)	(of space) behind, back, backwards. (of time) afterwards, after (with accusative) (of space) behind. (with accusative) (of time) after, since, (transf.) besides, except.
postea	Latin (lat)	Afterwards, hereafter, thereafter. Next, then.