The term 'unable' can be defined as lacking the ability, capacity, or means to do something. This is reflected in the crossword solutions provided, such as 'INEFFICIENT' (11 letters), which means not producing desired results; 'INADEQUATE' (10 letters), which means not sufficient; 'UNFITTED' (8 letters), which means not suitable; 'incapacitated' (13 letters), which means deprived of strength or ability; 'INAPT' (5 letters), which means not suitable; 'IMPOTENT' (8 letters), which means lacking power or authority; 'INEPT' (5 letters), which means not suitable or competent; 'USELESS' (7 letters), which means having no useful purpose; 'INEFFECTIVE' (11 letters), which means not producing a desired or intended result; 'UNQUALIFIED' (11 letters), which means not having the necessary skills or qualities; 'UNSKILLED' (9 letters), which means not having or showing any skill; 'INCOMPETENT' (11 letters), which means not having the necessary ability or knowledge; 'HELPLESS' (8 letters), which means unable to help oneself; 'UNFIT' (5 letters), which means not suitable; 'INCAPABLE' (9 letters), which means not having the necessary ability or qualities; and 'POWERLESS' (9 letters), which means lacking power or authority. All of these words describe the inability to do something, thus summarizing the term 'unable'.