What is it about words like "actor" and "waiter" that causes them to be considered male, so that they have female counterparts (i.e. "actress" and "waitress")?
Why are they not gender-neutral like "doctor" or "nurse" or "manager"?
Latin has auctor which gave English author. Another example is senator. The suffix -tor was used for male persons. A variant of -tor is Latin -ter as in pater (father). The o in -or was weakened to e. For female persons Latin had a special suffix -trix from -torix as in genetrix, victrix.
The suffix -trix, genitive -tricis, accusative -tricem became -tresse in French as in maîtresse and -tress in English as in waitress.
Why are there words such as doctor, teacher, student that can be used for male and female persons? Well, languages aren't designed at the drawing board and some words were taken in their Latin or French form, others were used for both sexes without a special ending which is not impractical.
A language has a development of thousand years and more and especially in word formation there are often several systems due to various origins.
Originally (or at least early in the time of Shakespeare up until 1660) only men were allowed to act on stage, young boys played the female parts.
Some interesting info can be found here http://www.elizabethan-era.org.uk/elizabethan-actors.htm
The word actress meaning a stage player is noted in the OED from 1666.
Similarly, waiters, in the sense of waiting on paying customers, were almost always men and used from the mid 17th century onward. As the OED states
- A man employed, at inns, hotels, eating-houses, or similar places, to wait upon the guests (esp. during meals). Also a man hired for a similar purpose on special occasions to supplement the staff of a private household.
The word waitress, in the same sense, is noted from 1834.
Doctor, in the sense of a medical professional, has been around since the 14th century but the rarely used (nowadays) Doctress/Doctoress is mentioned from the late 1500s right up to the late 19th century.
Nurse is actually much more feminine. As the OED states (in use from 1590)
3.a. A person, generally a woman, who attends or waits upon the sick; now esp. one properly trained for this purpose.
but the verb to nurse is from the mid 18th century, which is around the time that the modern idea of nursing came into being, rather than just helping the dying to die with some dignity. This wikipedia timeline clearly shows that nurses were usually women. http://en.wikipedia.org/wiki/Timeline_of_nursing_history.
As nurse is so associated with women there is a term male nurse which is defined at CollinsDictionary.com as
a male who is employed to tend the sick, injured or infirm; a nurse who is male