Otherwise known, in English, as August.
-ts’ósí, as you see in the end of the word, is in reference to something that is skinny, or lean.
When said as a whole, the direct translation stems from the Navajo word nit’ą́ (ripe, it is). It’s form is altered to reflect the plural and perfective (completed – or “past tense”) characteristic of a crop of ripened things.
So, it could be said that August is the time that the harvest starts, but not is not yet in full swing.