An archaic or dialectal term for a type of plant, possibly a water plant or herb, whose exact modern identification is uncertain.
From Old English 'hern' (heron) + 'sew' or 'seow' (possibly meaning plant or herb). The etymology is obscure, but the name might derive from association with herons or wetland plants where herons live.
Hernsew is one of those wonderfully obscure medieval plant names that scholars still debate about—we're not even entirely sure which modern plant it refers to, making it a fun mystery in botanical history!
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