tough proposition (?.)
- Augean task
- Chinese puzzle
- Herculean task
- backbreaker
- baffling problem
- ballbuster
- bitch
- brain twister
- chore
- crossword puzzle
- crux
- dead lift
- enigma
- enigmatic question
- floorer
- handful
- hard job
- hard pull
- heavy sledding
- jigsaw puzzle
- knot
- knotty point
- large order
- man-sized job
- mind-boggler
- mystery
- nut to crack
- perplexed question
- perplexity
- poser
- problem
- puzzle
- puzzlement
- puzzler
- question
- question mark
- rough go
- sixty-four dollar question
- sticker
- stumper
- tall order
- tough job
- uphill work
- vexed question
- why
