| fluctuate | shift back and forth |
| futile | unproductive |
| hostile | unfriendly |
| hypocrite | who fakes virtue |
| hypothesis | tentative assumption made in order |
| immense | enormous |
| impose | compel |
| indifferent | without interest |
| indulge | pamper |
| inevitable | incapable of being avoided |
| infer | hint |
| innocuous | inoffensive |
| innovate | introduce something new |
| intense | extreme |
| manipulate | to control skillfully |