Yes. The full clue is "From the Sioux tribe meaning "ally" (4 letters)". I can find nothing to fit in with the letters that I have from other clues - a?g?, and I feel sure that those are correct. Perhaps there is a compiler's error !!!
9 Down is "Round yellowish seeds of major food value - 9 letters", for which I have "chickpeas", which not only fits with other clues, but gives the letter "a".
6 Down is "Nickname given to a John Osbourne character - 5, 5, and 3 letters", for which I have "angry young man" to use the second letter "g".It leaves "a?g?" unsolved !
NORTH AND SOUTH DAKOTA. Taken from the Sioux word for “friend,” or “ally.” that is the history of place names I know , but also Dakota/Lakota had links with the Algonquin Indians so maybe a derivative of that - Algo??