leading — made of or containing lead: a lead pipe; a lead compound.
first — being before all others with respect to time, order, rank, importance, etc., used as the ordinal number of one: the first edition; the first vice president.
adv later on
before — If something happens before a particular date, time, or event, it happens earlier than that date, time, or event.
earlier — in or during the first part of a period of time, a course of action, a series of events, etc.: early in the year.
