Generally lowercase; capitalize when used as the proper name of the planet. “What on earth are you talking about?” The astronauts returned to Earth.
See affect, effect.
Use it to mean one or the other, not both. Correct: She said to use either door. Incorrect: There were lions on either side of the door. Correct: There were lions on each side of the door. There were lions on both sides of the door.
The nouns that follow these words do not constitute a compound subject; they are alternate subjects and require a verb that agrees with the nearer subject: Neither they nor he is going. Neither he nor they are going.
Avoid using as a verb: He emailed her the instructions. Preferred: He sent the instructions to her in an email message; He sent the instructions to her via email. Also, see computer terminology.
emeritus, emerita, emeriti
This word often is added to formal titles to denote that individuals who have retired retain their rank or title. When used place "emeritus" after the formal title, in keeping with the general practice of academic institutions: Professor Emeritus of Religion Robert Albertson, Professor Emerita of Comparative Sociology Ann Neel.
See accept, except.