| industry |
| inexorability(noun, perseverance, obstinacy, stubbornness, inflexibility) |
| inexorableness(perseverance, obstinacy, stubbornness, inflexibility, rigor) |
| inflexibleness(noun, perseverance, obstinacy, stubbornness, inflexibility) |
| integrity(noun, honor, perseverance, reliability, faithfulness) |
| intestinal fortitude(noun, expression, strength, energy, spirit) |
| intolerance |
| intractability(noun, obstinacy, stubbornness, inflexibility, mulishness) |
| intransigency(noun, perseverance, obstinacy, stubbornness, inflexibility) |
| intrepidity(noun, drive, energy, resolve, determination) |
| iron will(noun, expression, resolve, determination, resolution) |
| mettle(noun, spirit, determination, firmness, decision) |
| moxie(noun, strength, energy, spirit, resolve) |
| nerve(noun, drive, energy, spirit, resolve) |
| obstinance(noun, resolve, determination, resolution, firmness) |
| perseveration |
| plodding |
| plugging |
| preoccupation |
| principle(noun, honor, perseverance, reliability, faithfulness) |