But as Amos Chacham points out in Daat Mikra to Shmot 6:15, this was not the original meaning of either of the names. There are those (such as the Vilna Gaon) that claim on the basis of Divrei HaYamim I 8:3 and 8:6 that the original name was אחוד Echud - and the chet became a heh. This approach says the name relates to "unity".
The second approach brought by Chacham is that the name is related to hod הוד - "glory".
So where did the connection between אהד and sympathy develop? This was actually one of Ben-Yehuda's innovations. Moshe Nahir writes about Ben-Yehuda's way of creating new words:
His major source was the Bible, from which he drew dormant words, often assigning them new meanings (e.g., /kidma/, 'progress', from biblical Hebrew "east"), and roots (e.g., /ma'abada/, 'laboratory' from the root of biblical Hebrew /avad/, 'to work'), including ones he derived from biblical personal names (/ahad/, 'a.h.d', from Ohad, Ehud, cognate of Arabic "hawada", 'treat with kindness').
Klein writes that hawada means "he was indulgent". I can't find a Hebrew cognate for hawada, but if any reader knows of one, please let me know...