Atmosphere
Barometer.
intriguing
Their is not another name for HIV that starts with an R. That said, HIV is a type of retrovirus. That is probably the word you are looking for.
Another name for air resistance is aerodynamic drag.
Another name of a dog house is a kennel.
Rubella is another name for German measles.
Gaucho?
brew
S.o.s
Repast
inclement
Botany.