What is although in this sentence the book more than 50 years old it still contained helpful information?

In the sentence "Although the book is more than 50 years old, it still contained helpful information", the word "although" is a conjunctive adverb that introduces a concession.

Here's a breakdown:

* Conjunctive adverb: A word that connects two independent clauses while showing a relationship between them (like contrast, cause/effect, etc.).

* Concession: Acknowledging a contrasting or opposing point.

In this sentence, the two clauses are:

1. The book is more than 50 years old. (This suggests the book might be outdated)

2. It still contained helpful information. (This suggests the book is valuable despite its age)

"Although" signals that the second clause is surprising or unexpected given the information in the first clause. It's like saying, "Despite the fact that the book is old, it was still useful."