The two are synonyms when they are used as a conjunction with the meaning of "despite the fact that ...".

The difference is that "although" is used only as a conjunction and nothing else, while "though" has a wider usage.

"though" can be used as an adverb in the sense of 'however':  "He is good at math though".

"though" also makes phrases like "even though" (similar to "although") and "as though" (synonym to "as if").