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1. To become less dense in a particular area; to scatter or spread out. You can tell how high up the mountain you're going by how much the vegetation begins thinning out. I think you're better off waiting until September before you travel to Barcelona, let all the tourists thin out a bit before you arrive.
2. To dilute something; to make something less concentrated. In this usage, a noun or pronoun can be used between "thin" and "out." Try thinning the sauce out with a little bit of low-fat yoghurt. I swear the bartender is thinning out our drinks, because this tastes like nothing but soda.
3. To reduce the number of people or things some group or population. In this usage, a noun or pronoun can be used between "thin" and "out." Hunters have been hired to thin out the herds of deer roaming the state. The horrible outbreak thinned the country's population out by nearly half in the space of just 5 years.
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?
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.
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.