Sin is the Navajo word for the noun song. It is pronounced essentially the same as the English verbalisation.
Songs in Navajo are almost always meant to be sung, rather than simply played on an instrument. That is to say that almost every song, up until recently, was heavily laden with lyrics and extreme vocal ranges. Often times, a simple drum was the only instrument available for these songs. These traditional-type songs are often synonymous with a prayer of some sort, or else a kind of memory that is meant to be passed on.