Angst, depending on the context, may have different meaning. In this write up, I will broadly discuss both the scholary and colloquial use of the term. However, I will start by describing the etymology of the word. start by describing the etymology of the word.

Angst is a word occurring in German, Dutch, and the Scandinavian languages. In German¹ and Dutch it means fear, nothing more, nothing less. The word actually has its roots in Latin², specifically the word angustus³, which means narrow or confined. The Dutch word eng also reflects this, as this word can mean both scary and confined. Imagine how fear makes your chest feel all clenched up, if you will.

The word angst was introduced in the English language in 1849 by George Elliot⁴. Its use became popular by the the translation of the works of existentialist philosophers. For them, the concept of angst meant a deep and essentially philosophical anxiety about the world in general or personal freedom ⁵. The word was used between quotes to indicate it was jargon.

In the 1940s, the word came into more general usage. In particular, the phrase teenage angst caught on. If you would have to use a synonym for angst in this context, anxiety would come close-which is not surprising given the similar etymology. Generally, it means something like a general state of fear and depression. Wallowing in self-misery is implied, and the term is generally a pejorative.

In summary, angst started out as a specific piece of existentialist jargon, introduced into the English language in the middle of the 19th century. It generally lost its specific meaning, and became a general descriptor of anxiety with some depression mixed in⁵.

Sources:

1. My (t)rusty high school German
2. And you thought high school Latin was useless?
3. http://www.lieverleven.be/website/index.php?link=woordenboek. php&idwoord=277&woord=a
4. http://www.randomhouse.com/wotd/index.pperl?date=20000801
5. http://www.answers.com/topic/angst-1
6. Thank you jessicapierce