Historically this root seems to have referred to various plants, in particular the centaury, henbane and hemlock. All Scottish Gaelic incidents of this root collected in actual field-work (Lhuyd ettiô, DASG, Dieckhoff tetheotha) gloss it as hemlock. Dineen and O'Reilly gloss deodha as 'henbane', which may be the source of various entries in Scottish Gaelic dictionaries which gloss some of the forms of deodha as 'henbane'.

Old Irish glosses give dedga/deadhgha as meaning 'centaury' but note that this was an ambiguous term in older usage referring at least to two distinct plant families, centaurea or centaurium.

Henbane is rare in Scotland, especially in Gaelic-speaking areas, so the name may have transferred from an earlier plant to the much more common hemlock.