The word that would not be an appropriate synonym for the w...

"Although" needs to be connected to other sentence in the same period, it can not be alone.

For example:

Correct> Although she bought the car, she never used it.

Wrong> He bought flowers. Although she does not like them.

used for introducing a statement that makes the main statement in a sentence seem surprising

Although/though are subordinating conjunctions used to connect a subordinate clause to a main clause, like after, as, before, if, since, that, even though, even if.