Definition of re- in English:
from Latin re-, red- 'again, back'.
In modern English, the tendency is for words formed with prefixes such as re- to be unhyphenated: reacquaint, reconsider, reshape. For the sake of clarity, however, hyphenation is sometimes favored when the root word begins with a vowel: re-elect, for instance, may be preferred as a less awkward spelling than reelect. A hyphen is often used when the word formed with the prefix would be identical in form with, but different in meaning and pronunciation from, an already existing word: re-cover (meaning ‘cover again,’ as in we decided to re-cover the dining-room chairs), as opposed to recover (meaning ‘get better in health’).