The story
Compound of devil + -'s + nettle, perhaps for a stinging effect of the leaves, and/or for an association with the Devil or witches (see quotations below).
Etymology from Wiktionary, CC BY-SA 4.0.
devil's nettle
Today it means: Achillea millefolium or common yarrow, a flowering plant native to temperate regions of the Northern Hemisphere. Full definition →