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to spread out; to become less dense. The trees began to thin out as we got higher up the mountain. The crowd began to thin out as we got a little farther from the theater.
thin something out
to make something less dense; to scatter something. You will have to thin the young plants out, because there is not room for all of them. Can you thin out these young plants?
1. To make something less dense or concentrated: A harsh winter thinned out the herd of deer. The chef thinned the sauce out with water.
2. To become less dense or concentrated: The air thinned out as we climbed up the mountain.