What was the first abstract term Helen Keller learned to understand? What abstract term took a long time to understand?

Helen describes learning about abstract terms in Chapter 6. The two specific concepts she writes about here are “love” and “think.”
It took her a while to understand what “love” is. After all, such an emotion is a difficult concept to explain, under any conditions. One day when they were outside, Anne Sullivan put her arm around her and spelled into Helen’s hand, “I love Helen.” This began Helen’s questions back to her teacher, trying to figure out exactly what “love” was.” Was it the aroma of flowers? No. Was it the warmth of the sun? No. “Her words puzzled me very much because I did not then understand anything unless I touched it,” Helen writes. Up to this point, she had learned only concrete words referring to physical objects.
In the midst of several days of pondering over the term “love,” Helen was engaged in the hands-on activity of stringing beads together by shape and size. Unfortunately, she had made mistakes in the pattern she was supposed to follow. Anne touched Helen’s forehead and spelled out the word “think.” “In a flash I knew that the word was the name of the process that was going on in my head,” Helen writes. “This was my first conscious perception of an abstract idea.” So, “think” is the answer to your first question.
This success prompted her to again tackle the idea of “love.” Eventually, after more questions to Anne, Helen understood the word and the concept. So, “love” is the answer to your second question. But Helen actually dealt with both of the terms at the same time.