Whenever in Sanskrit there is an "s", in ancient Persian it changes into "h", so that "Sindhu" became "Hindu"; and you are all aware how the Greeks found it hard to pronounce "h" and dropped it altogether, so that we became known as Indians.
Swami Vivekananda in: The Complete Works of Swami Vivekananda ( Vol 1-9 ) [ Kartindo Classics], p. 78.