Hidden, p. p. & a.
from Hide. Concealed; put out of view; secret; not known; mysterious. Hidden fifths or octaves (Mus.), consecutive fifths or octaves, not sounded, but suggested or implied in the parallel motion of two parts towards a fifth or an octave.
Syn. -- Hidden, Secret, Covert. Hidden may denote either known to on one; as, a hidden disease; or intentionally concealed; as, a hidden purpose of revenge. Secret denotes that the thing is known only to the party or parties concerned; as, a secret conspiracy. Covert literally denotes what is not open or avowed; as, a covert plan; but is often applied to what we mean shall be understood, without openly expressing it; as, a covert allusion. Secret is opposed to known, and hidden to revealed. Bring to light the hidden things of darkness. 1 Cor. iv. 5. My heart, which by a secret harmony Still moves with thine, joined in connection sweet. Milton. By what best way, Whether of open war, or covert guile, We now debate. Milton.
Shades of meaning
Fernald has no entry of its own for hidden; he lists it under mysterious, obscure.
Where he writes about it:
Hide is the general term, including all the rest, signifying to put out of sight or beyond ready observation or approach; a thing may be hidden by intention, by accident, or by the imperfection of the faculties of the one from whom it is hidden; in their games, children hide the slipper, or hide themselves from each other; a man unconsciously hides a picture from another by standing before it, or hides a thing from himself by laying something else over it. — from hide
A house is hidden by foliage; the bird's nest is artfully concealed. — from hide
Anything which is effectually covered and hidden under any mass or accumulation is buried. — from hide
Whatever is buried is hidden or concealed; but there are many ways of hiding or concealing a thing without burying it. — from hide
That is mystic or mystical which has associated with it some hidden or recondite meaning, especially of a religious kind; as, the mystic Babylon of the Apocalypse. — from mysterious
That is secret which is intentionally hidden. — from mysterious
In that which is abstruse (L. abs, from, and trudo, push) as if removed from the usual course of thought or out of the way of apprehension or discovery, the thought is remote, hidden; in that which is obscure there may be nothing to hide; it is hard to see to the bottom of the profound, because of its depth, but the most shallow turbidness is obscure. — from obscure