In seinem Kommentar zum biblischen Schöpfungsbericht schreibt der mittelalterliche Gelehrte Abraham ibn Esra:
ereb, Abend, is similiar in meaning to choschek, Finsternis.
It is called so because during this time of day forms blur together.
boker, Morgen (in contradistinction) is called so since one is able to distinguish them.
The root boker has the meaning investigation.
Commentary on the Creation, ed. Michael Linetsky 1998