Difference between sort -u and uniq -u

I always have been using sort -u to get rid of duplicates until now. But I am having a real doubt about a list generated by a software tool. The question is: is the output of sort -u |wc the same as uniq -u |wc? Because they don't yield the same results. The manual for uniq specifies: > -u, --unique only print unique lines My output consists of 1110 words for which sort -u keeps 1020 lines and uniq -u 1110 lines, the correct amount. The issue is that I cannot visually spot any duplicates on the list which is generated by using > at the end of the command line, and that there IS an issue with the total cracked passwords (in the context of customizing john the ripper).