challenging

Concise Oxford English Dictionary © 2008 Oxford University Press:
challenge/ˈtʃalənʤ/

▶noun

• 1 a call to someone to participate in a contest or fight to decide who is superior.

  ■ a demanding task or situation.

  ■ an attempt to win a sporting contest.

• 2 a call to prove or justify something.

• 3 Medicine exposure of the immune system to pathogenic organisms or antigens.

▶verb

• 1 dispute the truth or validity of.

  ■ Law object to (a jury member).

  ■ (of a guard) order (someone) to prove their identity.

• 2 invite (someone) to engage in a contest or fight.

  ■ make a rival claim to (a position).

  ■ (usu. as adj. challenging) test the abilities of.

• 3 Medicine expose (the immune system) to pathogenic organisms or antigens.

– derivatives
challengeable adjective,
challenger noun,
challengingly adverb.

– origin ME: from OFr. chalenge (n.), chalenger (v.), from L. calumnia ‘calumny’, calumniari ‘calumniate’.