Smallpox and Small pox

Smallpox noun - A highly contagious viral disease characterized by fever and weakness and skin eruption with pustules that form scabs that slough off leaving scars.

Small pox and smallpox are semantically related. In some cases you can replace phrase "Small pox" with "Smallpox", this terms are similar.

Smallpox and small pox are semantically related. You can use "Smallpox" instead a noun phrase "Small pox".