One of the mysteries of the English language finally explained.
After the due date, after the time in question; usually in the context of litigation about debt.
Early 17th century (in an earlier sense). From post-classical Latin post diem (in e.g. solvit post diem) from post after + diem, accusative of diēs day.
post diem/ˌpəʊs(t) ˈdiːɛm/
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