from ppl. stem of Latin rigāre cf. irrigate
1657 - Renodaeus' Medicinal Dispensatory, Richard Tomlinson;
see Example below
From: A Medicinal Dispensatory: Containing the Whole Body of Physick,
Composed by the Illustrious Renodaeus.
Chief Physician to the Monarch of France,
And Now Englished and Revised by Richard Tomlinson of London, Apothecary, 1657
The Second Book of Medicinal Matter, Of Minerals