In 12th century the Old French word
was imported into the German language. In Middle High German it soon became
and soon (still in Middle High German) v turned into b:
And in New High German it turned into
So this word has absolutely no connection to »der Abend« (the evening) or »teuer« (expensive).
But also the Old French word "aventure" was not invented by Old French native speakers. It has a Latin root, which is
This word means »what soon will happen«. Also the German word »der Advent« and the English word "advent" (the time before christmas) derive from adventura.
But the latin "adventura" also was adopted by English language in a second way: It also is the root of "adventure". So German »Abenteuer« and English "adventure" are siblings with the same parent, and this is true for "advent" too.
Just to show, that »der Abend« is not a member of the family grown from the root adventura:
- New High German
- Middle High German
- Old High German
Linguists believe, that this word derived from the indo-european preposition *epi which not only means after, but also is the root of the English word after. So German »Abend« and English "after" are siblings. They are not related to »Abenteuer« or "adventure".
The old Germans obviously thought of the evening as the later part of the day.
The word »teuer« was in Middle High German »tiure« and in Old High German »tiuri«. But linguists have no idea, how and from where »tiuri« became a part of German language.
So, the second part of »Abenteuer« also in the 12th century was identical to the root of »teuer«. But before that time there was no equivalent of »Abenteuer« in German language, whereas »tiuri« also existed in German in 9th century.