thin
v. A2 Elementary Oxford US //ˈθɪn// UK //θˈɪn// thin
v. to make something less thick or crowded. You can do this by adding liquid to a sauce or by removing some plants from a garden.
v. to reduce the thickness, density, or number of something. Often used with 'out' when referring to the removal of individual items from a group to create more space.
You should thin the paint with a little water.
The gardener needs to thin out the carrots so the remaining ones have enough room to grow large.
As the hikers climbed higher into the mountains, the oxygen began to thin, making every step feel significantly more exhausting than it had at sea level.
Usage
Often functions as a phrasal verb 'thin out' when referring to crowds or plants. When used with liquids, it typically takes 'with'.