1. To join, unite, or blend into some larger group or body. Be sure to give cars a wide berth when they're merging into the highway from a side road. There's a stream that merges into the main river about 100 kilometers from here—that's where we can nab the bandits. The two smaller companies merged into a more powerful corporation.

2. To cause someone or something to join, unite, or blend into some larger group or body. In this usage, a noun or pronoun is used between "merge" and "into." Our plan is to take the two departments and merge them into one—that way we can reduce our staff numbers and save on costs. Because of the accident, police merged everyone in the left lane into the right one.