Contagious
Etymology
From Latin "contagio" (a touching, contact), from "com-" (together) and "tangere" (to touch) — the same root as "tactile" and "contact." The original image is of catching something by touch, person passing to person.
adjective · /kun-TAY-jus/
Able to spread from one person to another, especially by contact.
What it names
Reach for it when you mean a disease that jumps between people — not merely one caused by a germ.
Example
Chickenpox is highly contagious, so she stayed home until the spots crusted over.
Related idea
Every contagious disease is infectious, but not every infectious disease is contagious. Tetanus and malaria are infectious — caused by pathogens — yet not contagious, because you can’t catch them from another sick person; you need the soil or the mosquito.