difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge; "the professor's lectures were so abstruse that students tended to avoid them"; "a deep metaphysical theory"; "some recondite problem in historiography"
requiring more than usually expected or thought due; especially great patience and effort and skill; "found the job very demanding"; "a baby can be so demanding"
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"
marked by unjust severity or arbitrary behavior; "the oppressive government"; "oppressive laws"; "a tyrannical parent"; "tyrannous disregard of human rights"
weighing heavily on the senses or spirit; "the atmosphere was oppressive"; "oppressive sorrows"
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"
move downward and lower, but not necessarily all the way; "The temperature is going down"; "The barometer is falling"; "The curtain fell on the diva"; "Her hand went up and then fell again"
the act of improving something (especially machinery) by raising it to a higher grade (as by adding or replacing components); "the power plant received a new upgrade"
hardware that provides better performance than an earlier version did
the property possessed by a slope or surface that rises
a reservation that is improved; "I got an upgrade to first class when coach class was full"
software that provides better performance than an earlier version did
to improve what was old or outdated; "I've upgraded my computer so I can run better software"; "The company upgraded their personnel"
give better travel conditions to; "The airline upgraded me when I arrived late and Coach Class was full"
get better travel conditions; "I upgraded to First Class when Coach Class was overbooked"