This is the 6391st most frequent Arabic word.
اثنتين
"اثنتين" means "two" (feminine form).
The word "اثنتين" is used to denote the numeral "two" in the feminine form to match the gender of "كتب" (books), which is a feminine plural noun.
لديّ اثنتين من الكتب على الطاولة.
I have two books on the table.
Here, "اثنتين" adjusts to the feminine gender of "أدوات" (tools), indicating two items.
تحتاج إلى اثنتين من الأدوات لإتمام العمل.
You need two tools to complete the work.
In this sentence, "اثنتين" correlates with "أمور" (matters), which is treated as feminine in Arabic.