1) Arduous 2) Burdensome 3) Burdensome, not easily borne 4) French word used in English 5) Galling 6) Hardly a cakewalk 7) Heavy 8) Not easily borne 9) Number turning sour and heavy 10) Oppressive 11) Oppressive, difficult to bear 12) Taxing 13) Troublesome 14) Trying 15) Wearing 1) Backbreaking 2) Burdensome 3) Difficult 4) Taxing 
• (a.) Burdensome; oppressive.
On'er·ous adjective [ Latin onerosus , from onus , oneris , a load, burden: confer French onéreux .] Burdensome; oppressive. 'Too onerous a solicitude.' I. Taylor. Onerous cause (Scots Law) , 
needing effort burdensome 
onerous (ON uhr uhs, OH nuhr uhs) 1. Representing a great burden or much trouble. 2. Involving obligations that are more disadvantageous than advantageous. 3. Troublesome or oppressive; burdensome. 4. The figuratively heavy load imposed by something irksome or annoying. 5. Having or involving obligations or responsibilities; especially, l...
[SAT terms] not easily borne; wearing[Literary terms] burdensome or difficult to endure not easily borne; wearing