An open or sealed letter, from a merchant in one place, directed to another, in another place or country, requiring him, if a person therein named, or the bearer of the letter, shall have occasion to buy commodities , or to want money to any particular or unlimited amount, either to procure the same or to pass his promise, bill, or bond for it, the writer of the letter undertaking to provide him the money for the goods, or to repay him by exchange, or to give him such satisfaction as he shall require, either for himself, or the bearer of the letter. 3 Chit. Com. Law, 336. A letter of credit is a written instrument , addressed by one person to another, requesting the latter to give credit to the person in whose favor it is drawn. Civ. Code Cal.