R. Eliezer says: It was like "haggadah" (from "gad"), which "pulls" a person's heart. Others say: It testifies ("maggid," from "gad") about itself that it is manna, for it falls neither on Sabbath, or festival, or Yom Kippur.
Rabbi Eliezer Connects the Manna to the Word Haggadah Non-legal
Mekhilta Tractate Vayassa 6:8