The first occurrence.
And God called the firmament Heaven. And the evening and the morning were the second day. Gen 1:8
The primitive root.
shin ש = two front teeth, thus sharp, press, eat, two, again
nun נ ן = the seed, thus continue, heir, son
hey ה = man with upraised arms, thus look, reveal, wonder, worship, breath
The story: Something happened once, and now a second (shin) time, so that it continues (nun) to be evident (hey, in the sense of being pointed out).