I think 'tie the knot' originated from British troops and merchants stationed in India centuries ago. South Indian Hindu weddings have an auspicious time calculated by the astrologers for "tieing the knot" ie, the time when the groom ties the knot of the wedding pendant of the bride. Invitations to Hindu weddings even specify the time for this part of the ceremony. Since the English were in India from at least the 1600's this would allow for ample time to enter into the English language. What do you think?