expression, godan verb (-ru)
be at one's wit's end; be at a loss what to do
Used when one has thought hard but still cannot find a solution or make a decision. Often implies a difficult problem or dilemma.
どうすればいいか思案に余っている。
I'm at my wit's end about what to do.
彼はその難問に思案に余った。
He was at a loss over that difficult problem.