Pronunciation: seye-DAHR, seye-DEEN
Saidar is the female half of the True Source and saidin is the male half of the True Source. Only a man can draw on saidin, only a woman on saidar.
Saidin is fouled by the taint of the Dark One, like a thin slick of rancid oil on water. The water is still pure, but it cannot be touched without touching the foulness. (TEotW,Ch12) Their bonds, oaths and ties to the Great Lord protect the male Forsaken from the taint. (TFoH,Prologue)