inspiring fear; "the formidable prospect of major surgery"; "a tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic"- G.H.Johnston; "something unnerving and prisonlike about high grey wall"
extremely impressive in strength or excellence; "a formidable opponent"; "the challenge was formidable"; "had a formidable array of compositions to his credit"; "the formidable army of brains at the Prime Minister's disposal"
a rocket-propelled guided missile that can escape the earth's atmosphere; makes observations of the solar system that cannot be made by terrestrial observation
not easy; requiring great physical or mental effort to accomplish or comprehend or endure; "a difficult task"; "nesting places on the cliffs are difficult of access"; "difficult times"; "a difficult child"; "found himself in a difficult situation"; "why is it so hard for you to keep a secret?"
requiring much effort and trouble; "the mountain climb was long, steep, and difficult"
(mathematics) a set of entries in a square matrix running diagonally either from the upper left to lower right entry or running from the upper right to lower left entry
an oblique line of squares of the same color on a checkerboard; "the bishop moves on the diagonals"
a line or cut across a fabric that is not at right angles to a side of the fabric
(geometry) a straight line connecting any two vertices of a polygon that are not adjacent
at an angle; especially connecting two nonadjacent corners of a plane figure or any two corners of a solid that are not in the same face; "a diagonal line across the page"