challenging Synonyms

ambitious intriguing thought-provoking recuse rejoining resisting rough scuffling severe significative stimulant stimulating rebuffing rebelling questioning interrogating laborious mettled onerous opposing problematic problematical protesting provocative question stimulative trying antiauthoritarian labor-intensive brain surgery long-range call into question newsworthy hurdlesome problematically recusal repressing duelling gruelling taxing testing toilsome tough tricky uphill upstream weighty call out grueling strenuous