second: the one that comes next after the first in a sequence, in time, or in rank
This is the ordinary counting word "second," the number you reach right after "first." It points to whatever follows next: the second river, the second son, the second row of stones, the second chariot in a line.
It does the same work with time. The Bible uses it constantly for the second day, the second month, and the second year, which is why it turns up so often in the creation account, the calendar laws, and the dated records of kings and priests.
The feminine form also slides into an everyday adverb. Instead of naming "the second" of something, it can simply mean "a second time" or "again," as when the word of the Lord comes to a prophet a second time, or an angel calls out again. Underneath all of these is one plain idea: not the first, but the next one after it.