This is the 2985th most frequent Arabic word.
أحدهما
"One of them."
Here, "أحدهما" is used to refer to one member of a specifically mentioned pair for emphasis and focus.
رأيتُ طالبين، وأحدهما كان يحمل كتابًا.
I saw two students, and one of them was carrying a book.
In this case, "أحدهما" identifies one item from a set of two previously mentioned elements.
اخترتُ مسارين، وأحدهما أقصر من الآخر.
I chose two paths, and one of them is shorter than the other.
Here, "أحدهما" indicates one among the two subjects referred to in the sentence.