Synonyms of the word

unable

• adj. Not able; lacking a certain ability.

impotent

• adj. Lacking physical strength or vigor; weak.
• adj. Lacking in power, as to act effectively; helpless.
• adj. Incapable of sexual intercourse, often because of an inability to achieve or sustain an erection.
• adj. (of a male) Sterile.
• adj. (obsolete) Lacking self-restraint.
• n. A man who has erectile dysfunction.
• n. An impotent or powerless person.

incapable

• adj. Not capable (of doing something); unable.
• adj. Not in a state to receive; not receptive; not susceptible; not able to admit.
• n. (dated) One who is morally or mentally weak or inefficient; an imbecile; a simpleton.

ineffective

• adj. not having the desired effect; ineffectual.
• adj. lacking in ability; incompetent or inadequate.

ineffectual

• adj. unable or insufficient to produce effect; futile.
• adj. worthless.
• adj. weak, indecisive; lacking forcefulness.