(n.) The quality or state of being unable; lack of ability; want of sufficient power, strength, resources, or capacity.

disability disablement disqualification imbecility inadeptness inadequacy inaptitude inaptness inattentiveness incapability incapacitation incapacity incompetence incompetency indexterity ineffectiveness ineffectuality ineffectualness inefficiency ineptitude ineptness infancy inferiority insufficiency legal incapacity maladjustment maladroitness mediocrity minority pedestrianism rustiness skill-lessness thoughtlessness unaptness uncleverness undeftness undexterousness undextrousness unfitness unfittedness unintelligence unproficiency unschooledness unskillfulness untrainedness wardship