origin; source; history; originally; from the start; by nature
going through; going via; going by way of
an extremely great number (often said to be 100 million); 10^60 (or 10^72)
acquaintance; relation; affinity; reason
transit point; transit airport; connection airport
naturally-derived; naturally-occurring
anthropozoonosis (diseases transmitted to humans by animals)
connection; relationship; origin; reason; motive (e.g. for an act)
to let a chance to do something slip through one's fingers