An Etymological Dictionary of the German Language/Annotated/Keuschlamm
Keuschlamm, ‘chaste tree,’ simply Modern High German, formed from Middle Latin agnus castus, known in Greek by the term ἄγνος; this being associated with ἁγνός, ‘pure,’ gave rise to the Latin agnus castus; agnus, Greek ἄγνος, being confused with agnes, ‘lamb,’ led to High German Keuschlamm, one of the strangest products of sciolism (not of popular etymology). The tree is also called Keuschbaum, Dutch kuischboom.