初旬
しょじゅん · shojun · JLPT N2 · adverb
first 10 days of the month
初 (first) + 旬 (ten-day period): first ten days of the month
初 means first or beginning, and 旬 means a ten-day span, as in the three 旬 of each month. Put them together and you get the first ten days.
初 — clothes radical 衤 + knife 刀
初 combines 衤 (clothes) and 刀 (knife), depicting the act of cutting cloth to begin making a garment. From this concrete image of starting a tailoring task came the extended meaning 'beginning' or 'first'. It is an associative compound, not phonetic.