helpless(unable to act without help; needing help; feeble) adjective [UK: ˈhel.pləs] [US: ˈhel.pləs]
incapable(not being capable) adjective [UK: ɪnˈk.eɪ.pəb.l̩] [US: ˌɪnˈk.eɪ.pəb.l̩]She is incapable of deceit. = Ella es incapaz de engañar.
inept(not able to do something) adjective [UK: ɪ.ˈnept] [US: ˌɪ.ˈnept]This cloth has the special ability to be invisible to the stupid and the inept. = Esta tela tenía la característica especial de ser invisible para los estúpidos y los incapaces.
unable(not able) adjective [UK: ʌn.ˈeɪb.l̩] [US: ʌ.ˈneɪb.l̩]He is unable to do it. = Él es incapaz de hacerlo.