http://grammarist.com/grammar/agent-recipient-nouns/

An agent noun denotes a person who performs an action. Most agent nouns end in either  –er (standard) or –or (for words derived directly from Latin). A recipient noun denotes a person who receives an action. Recipient nouns usually have the suffix –ee, which technically means one to whom.

Examples

Agent nouns are more common than recipient ones simply because recipients need agents while agents do not need recipients. Here are just a few of the thousands of agent nouns in English:

• debtor
• director
• employer
• flyer
• lecturer
• payer
• performer
• prosecutor
• runner
• server
• teacher

There are far fewer established —ee words. Here are a few of the more common ones:

• employee
• evacuee
• honoree
• lessee
• payee
• trustee

Creating words with the –er, -or, and –ee suffixes

Each of these suffixes are living, which means they may be attached with no hyphen. Your spell check may catch coinages such as condemnee, directee, and lecturee, but these are perfectly good words if used well.

When creating recipient nouns, keep in mind that a recipient is one to whom something is given or one for whom something is done. So, for example, the relatively new word attendee, indicating one who attends, is questionable because one does not receive attendance. The word technically should be attender (but, of course, it’s not).

Creating –er and –or words can be tricky in a different way. The –er suffix is safer, as it can be applied to any solidly English word. The suffix –or is reserved for words that come directly from Latin. For example, prosecute comes from the Latin prosequi, so the English agent noun is prosecutor. Words that are further removed from their Latin roots often take the –er suffix. When in doubt, consult a dictionary.