challenging

(noun, adjective, verb)

adjective

1. requiring full use of your abilities or resources

- performed the most challenging task without a mistake

Similar word(s): difficult, hard, ambitious

2. stimulating interest or thought

- a challenging hypothesis

Similar word(s): stimulating

3. provocative

Similar word(s): provocative, intriguing

noun

1. The act of making a challenge.

verb

1. present participle of challenge