*Rēdagunþiz (Proto-Germanic) comes from Proto-Germanic rēdaz, from Proto-Indo-European Hréh₁dʰos, from Proto-Indo-European Hreh₁dʰ-, from Proto-Indo-European h₂reh₁-, from Proto-Indo-European h₂er- — to fit, to fix, to put together.
Ancestry of “*Rēdagunþiz”, step by step
*Rēdagunþiz traces back through two separate lines of ancestry.