People who don’t know much bout the Bible still know what “knowing in the biblical sense” means. It’s assumed that it’s a common euphemism.
But it isn’t. It’s used only in the first few chapters of Genesis, and then in 1 Samuel.
Adam knows Eve, and she conceives Cain (Genesis 4:1). Cain knows his wife, and she has a son, Enoch (4:17). Then Adam knows his wife again and she gives birth to Seth (4:25). The phrase isn’t used again until 1 Samuel 1:19, when Elkanah knows his wife Hannah, who gives birth to Samuel.
Second, the cluster of uses in Genesis 4 structurally matches the use in 1 Samuel. 1 Samuel is a new Genesis. After the “week” of seven books – Genesis to Judges/Ruth – Yahweh starts a new week with another miracle child. Another canonical cycle begins with another man knowing his wife in the biblical sense.