1. To join, unite, or blend in with someone or something else. Be sure to give cars a wide berth when they're merging with traffic on the highway. There's a stream that merges with the main river about 100 kilometers from here—that's where we can nab the bandits. Our company merged with another run by a friend of mine to form a single, more powerful corporation.
2. To cause someone or something to join, unite, or blend in with something else. In this usage, a noun or pronoun is used between "merge" and "with." They're merging our department with the marketing team to improve efficiency, or so they say. Because of the accident, police had to merge everyone in the left lane with the people in the right.
merge (something) with (something else)
to join two things together. The management merged the sales division with the marketing division. We merged the accounting department with the auditing department.
merge with someone or something
to join with someone or something. Ted merged with Fred and they created a very profitable partnership. Our company merged with a larger one, and we all kept our jobs. This stream merges with a larger stream about two miles to the west.