onerous (adj.)
- annoying
- arduous
- backbreaking
- bothersome
- burdensome
- crushing
- cumbersome
- cumbrous
- demanding
- difficult
- effortful
- exacting
- exhausting
- exigent
- forced
- grievous
- grueling
- hard
- hard-fought
- harsh
- heavy
- heavy-handed
- hefty
- impeding
- incumbent
- irksome
- killing
- labored
- laborious
- lumpish
- massive
- operose
- oppressive
- painful
- plaguey
- ponderous
- punishing
- strained
- strenuous
- superincumbent
- taxing
- toilsome
- tough
- troublesome
- trying
- tyrannous
- unruly
- unwieldy
- uphill
- vexatious
- wearing
- wearisome
- wearying
- weighty
