Immunity
Etymology
From Latin immunitas, "exemption from a duty or burden," from in-, "not," and munus, "service, obligation" (the root of "municipal" and "community"). It first meant being freed from a public tax or task — a sense that survives in "legal immunity." Medicine borrowed the idea of exemption for the body’s freedom from a disease it has learned to fend off.
noun · /ih-MYOO-nih-tee/
The body’s ability to resist a particular infection, having learned to recognize and fight it.
What it names
Why you usually catch chickenpox only once — the body keeps a memory of past threats and answers faster next time.
Example
After the infection, she had some immunity and shrugged off the next season’s bug.
Related idea
Contagion is the spread of disease; immunity is the body’s defense against catching it again.
noun · /ih-MYOO-nih-tee/
Legal exemption from a duty, penalty, or prosecution that would otherwise apply.
What it names
diplomatic immunity; immunity granted to a witness
Example
She testified only after being granted immunity from prosecution.
Related idea
From Latin “immunis” (exempt from public service); the medical sense borrowed the same idea of being exempt — here, from a disease.