challenging

(verb) take exception to. Synonyms: challenge, dispute, gainsay. Example: "She challenged his claims."

(verb) issue a challenge to. Synonyms: challenge. Example: "Fischer challenged spassky to a match."

(verb) ask for identification. Synonyms: challenge. Example: "The illegal immigrant was challenged by the border guard."

(verb) raise a formal objection in a court of law. Synonyms: challenge, take exception.

(adj) requiring full use of your abilities or resources. Synonyms: ambitious. Examples: "Ambitious schedule." "Performed the most challenging task without a mistake."

(adj) stimulating interest or thought. Synonyms: thought-provoking. Examples: "A challenging hypothesis." "A thought-provoking book."

(adj) disturbingly provocative. Synonyms: intriguing. Example: "An intriguing smile."