Etymology From Middle English dern, derne, from Old English dyrne, dierne (“hidden, secret, retired, obscure, remote, eluding detection, concealed, deceitful, evil, magical”), from Proto-West Germanic *darnī (“hidden, secret”). Doublet of terne.
Etymology From Middle English dernen, dærnen, from Old English dyrnan, diernan (“to keep secret, conceal, hide, restrain, repress, hide oneself”), from Proto-West Germanic *darnijan (“to conceal”), from *darnī (“hidden, secret”). Cognate with Old Saxon dernian (“to conceal”), German tarnen (“to camouflage, disguise”). See also darn, tarnish.
1855, Charles Kingsley, Westward Ho!, Ch. XIV, How Salvation Yeo Slew the King of the Gubbings So I just put my eye between the wall and the dern of the gate, and I saw him come up to the back door […]