Meaning

verb place (flax, hemp, or jute) in liquid so as to promote loosening of the fibers from the woody tissue

originFrom Middle English retten, reten; perhaps from Middle Dutch rēten, reeten (compare Middle Low German rōten; Middle High German rōzen), or from Old Norse reyta (compare Norwegian røyta, Swedish röta); all from Proto-Germanic *rautijaną (“to make mellow or soft”), from Proto-Indo-European *rewd- (“to tear; rend; rip”). Related to rot.

Etymology from Wiktionary, CC BY-SA 3.0