First Ten Days Of The Month
Beginning Of The Month
noun
What are the above ten days of the month? They're the first ten days of the month, of course, or even just the beginning of the month.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
気象庁は六月上旬に梅雨が始まると言っている。
The Japan Meteorological Agency says the rainy season will start at the beginning of June.