A ten-square should consist of ten different 10-letter words, all to be found in reputable dictionaries or perhaps gazetteers, arranged one under another so that the first row word is the same as the first column word, and so on, ie something like.
"My First Ten-Square,"
Word Ways: Vol. 35
, Article 2.
Available at: http://digitalcommons.butler.edu/wordways/vol35/iss3/2