| enervated(adjective, weak, uncertain, inadequate, feeble) |
| featherweight |
| feckless(adjective, inferior, inadequate, limited, feeble) |
| flaccid(adjective, uncertain, feeble, shaky, hesitant) |
| flimsy(adjective, uncertain, feeble, shaky, hesitant) |
| fruitless(adjective, inferior, inadequate, limited, feeble) |
| futile(adjective, inferior, inadequate, limited, feeble) |
| gutless(adjective, weak, inadequate, incompetent, inept) |
| idle(adjective, inferior, inadequate, limited, feeble) |
| indecisive(adjective, inferior, inadequate, limited, feeble) |
| inefficient(adjective, inferior, inadequate, limited, feeble) |
| inept(adjective, weak, inferior, inadequate, limited) |
| infecund(adjective, weak, inadequate, incompetent, inept) |
| inferior(adjective, inadequate, limited, feeble, useless) |
| innocuous(adjective, inferior, inadequate, limited, feeble) |
| inoperative(adjective, inferior, inadequate, limited, feeble) |
| invalid(adjective, enervated, meaningless, senescent, unsubstantiated) |
| invertebrate |
| irresolute(adjective, weak, soft, uncertain, feeble) |
| lame(adjective, inferior, inadequate, limited, feeble) |