Cross reference
Exodus 15:23
23 When they came to Marah, they couldn't drink from the waters of Marah, for they were bitter. Therefore the name of it was called Marah.{Marah means bitter.}
Numbers 33:8
8 They traveled from before Hahiroth, and passed through the midst of the sea into the wilderness: and they went three days' journey in the wilderness of Etham, and encamped in Marah.
Ruth 1:20
20 She said to them, "Don't call me Naomi, call me Mara; for the Almighty has dealt very bitterly with me.