Because.
Synonyms:
as, for, inasmuch as, since.
Because, literally by-cause, is the most direct and complete word for giving the reason of a thing. Since, originally denoting succession in time, signifies a succession in a chain of reasoning, a natural inference or result. As indicates something like, coordinate, parallel. Since is weaker than because; as is weaker than since; either may introduce the reason before the main statement; thus, since or as you are going, I will accompany you. Often the weaker word is the more courteous, implying less constraint; for example, as you request it, I will come, rather than I will come because you request it. Inasmuch as is a formal and qualified expression, implying by just so much, and no more; thus, inasmuch as the debtor has no property, I abandon the claim. For is a loose connective, giving often mere suggestion or indication rather than reason or cause; as, it is morning, for (not because) the birds are singing.
Antonyms:
altho, however, nevertheless, notwithstanding, yet.
Compare synonyms for BUT; NOTWITHSTANDING.