Not able; not having sufficient strength, means, knowledge, skill, or the like; impotent; weak; helpless; incapable; -- now usually followed by an infinitive or an adverbial phrase; as, unable for work; unable to bear fatigue.

Used to indicate that an order couldn't be filled/executed. Eg, “Your order in the Bonds was ‘unable'.

A working order which has not yet been able to be executed.

Is an indication report that the order, as given or when given, was unable to be executed. This can happen on a limit order where the market continues to trade at the limit price but there were other orders ahead of it on a time basis.

(usually followed by `to') not having the necessary means or skill or know-how; "unable to get to town without a car"; "unable to obtain funds"

(usually followed by `to') lacking necessary physical or mental ability; "dyslexics are unable to learn to read adequately"; "the sun was unable to melt enough snow"

lacking in power or forcefulness; "an ineffectual ruler"; "like an unable phoenix in hot ashes"