A problem that is challenging to solve.
Used other than figuratively or idiomatically: see hard, nut, crack.
A situation, person, group, etc. which is difficult to overcome or deal with.
A place, opportunity, etc. to which it is difficult to gain entry.
An amount that is difficult to finance.
A verbal puzzle, mystery, or other problem of an intellectual nature.
A board with a row of pins, set zigzag, between which wire is drawn to straighten it.
A sieve with coarse meshes, usually of wire, for separating coarser materials from finer, as chaff from grain, cinders from ashes, or gravel from sand.
An ancient verbal, poetic, or literary form, in which, rather than a rhyme scheme, there are parallel opposing expressions with a hidden meaning.
One of the pair of curtains enclosing an altar on the north and south.
To fill with holes like a riddle.
To speak ambiguously or enigmatically.
To fill or spread throughout; to pervade.
To put something through a riddle or sieve; to sieve; to sift.
To solve, answer, or explicate a riddle or question.