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.
Meanings
(dialectal, obsolete) Hidden; secret; private.
Now with their backs to the den's mouth they sit, / Yet shoulder not all light from the dern pit. 1659, Dr. H. More, Immortal, of the Soul:
Through dreary beds of tangled fern, / Through groves of nightshade dark and dern. 1819, J. R. Drake, The Culprit Fay:
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.
Meanings
(obsolete, transitive) To hide; secrete, as in a hole.
He at length escaped them by derning himself in a fox-earth. 1865, Hugh Miller, My schools and schoolmasters:
(intransitive, obsolete) To hide oneself; skulk.
But look how soon they heard of Holoferne / Their courage quail'd, and they began to derne. 1584, Thomas Hudson, Judith:
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 […]