The noun zeitgeist, meaning the spirit of the time, is a loanword from German (translating literally to time ghost).1 The word has been in widespread use for a long time (at least a century and a half),2 so it no longer needs to be capitalized or italicized.
Here are two examples of correct zeitgeist usage:
His desire to get under the skin of the establishment caught the zeitgeist, and to the young of the time he proved a striking standard-bearer for disaffection and change. [The Music Magazine]
The year 1964 was one of those moments when the reigning “ism” — abstract expressionism — had sputtered out, and the zeitgeist screamed for change. [Star Tribune]
Zeitgeist may also be used to denote the spirit of a specific group or movement, rather than of the age in general—for example:
Ten years ago the writer/director Justin Kerrigan burst on to the British film scene with the movie that most successfully tapped into the zeitgeist of the rave movement. [Times Online]
References
1. http://www.collinsdictionary.com/dictionary/english/zeitgeist ↩
2. Google Ngram for “zeitgeist,” 1800-2000 ↩
