Wiktionary
vb. 1 (context transitive English) To make sparse. 2 (context intransitive English) To become sparse.
WordNet
Usage examples of "thin out".
Crouching among the trees, which here commenced to thin out slightly, Bradley saw what appeared to be an enormous dragon devouring the carcass of a mammoth.
The trees began to thin out and we thought we were approaching the beach.
The Scotch say, that no man ought to thin out his own turnips, because he will not sacrifice enough to leave room for the remainder to grow: he should get his neighbor, who does not care for the plants, to do it.
The Matter was thin out there between the galaxies, but Ames gathered it, scraping it together over the cubic light-years, choosing the atoms, achieving a clayey consistency and forcing matter into an ovoid form that spread out below.
It was only when the trees began to thin out and he could see the open grassland ahead that he ordered a halt and trotted back to report to Kerrick.
With a cry, Larry threw his arm over his eyes and saw the pictures thin out, blur and dissolve.
Haves became smaller, were set farther apart, and the jungle began to thin out.
When about an inch high, thin out to 6 or 8 inches apart each way.
Sow the seed in May or June, in drills about 1 inch deep, about 12 inches apart, and thin out the young plants to 6 or 8 inches apart in the rows.