Both ALTHOUGH and THOUGH mean ‘in spite of something. Both are the same thing, and are replaceable with each other. For emphasis, we often use EVEN with THOUGH (but we can’t use EVEN with ALTHOUGH); e.g.

The match was beautiful although we lost it.
= The match was beautiful though we lost it.

INCORRECT: Even although she is very busy, she still found time to help me.
CORRECT: Even though she is very busy, she still found time to help me.

NOTE-I: When a sentence begins with ALTHOUGH or THOUGH, we don’t use BUT or YET before the main clause, we usually put a comma rather; e.g.

INCORRECT: Although he was late, yet he stopped to buy fruit.
CORRECT: Although he was late, he stopped to buy fruit.

NOTE-II: Don’t use ALTHOUGH or THOUGH in front of a noun phrase, you use IN SPITE OF or DESPITE instead in such a case; e.g.

INCORRECT: Although his hard work, he failed his exam.
CORRECT: In spite of his hard work, he failed his exam.

NOTE-III: THOUGH sometimes is an adverb. You use it when you are making a statement that contrasts with what you have just said. You usually put THOUGH after the first phrase in the sentence. ALTHOUGH is never used an adverb; e.g.

INCORRECT: Very nice although, this dress is too expensive.
CORRECT: Very nice though, this dress is too expensive.

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