auxiliary verb
cannot do; unable to do; impossible to do
Archaic or highly literary auxiliary verb equivalent to modern できない. Used after the continuative form (連用形) of a verb. In modern Japanese, it appears mainly in set phrases, classical quotations, or deliberately formal writing.
彼の努力も及ばず、ついに成し能わずして終わった。
Even his efforts fell short, and in the end he was unable to accomplish it.
古典では「言う能わず」のように使われる。
In classical texts, it is used like 言う能わず (unable to say).