久攻不下

to attack for a long time without success

(long) time / (long) duration of time

to attack / to accuse / to study

no; not so / (bound form) not; un-

to be not less than (a certain quantity, amount etc)

down / downwards / below / lower / later / next (week etc) / second (of two parts) / to decline / to go down / to arrive at (a decision, conclusion etc) / measure word to show the frequency of an action