Dan's explanation is really good and it comprises why even though
shy and timid have different uses in English, in Spanish it would
be just one word...
Well, I have to look at it the other way around hehehe So, I try to
use the differences between shy and timid in English so I could
find the right equivalent in Spanish. Correct me if I'm wrong:
Timidity connotes fear and being easily alarmed. A more informal
rendition would be "jumpy" - someone who jumps or startles easily,
for example upon hearing a loud unexpected noise.
Shyness connotes social reluctance, someone who is uncomfortable in
social situations, who doesn't like to talk to strangers; at
parties for example.
If search for tímido, then yes, you will find
timid and shy, But, using the different contexts,
if you want to refer to the timid definition, maybe you should use
"asustadizo", "temeroso" or