To be at a loss after thinking repeatedly; to rack one's brains in vain and fail to come up with a good idea or solution.
新しい企画についてチームで何時間も考えあぐねた。
The team racked its brains for hours over the new project idea.
彼女は適切な言葉を見つけられず、考えあぐねたまま黙っていた。
She couldn't find the right words and remained silent, still at a loss.
解決策が見つからず、最後は考え倦ねてしまった。
Unable to find a solution, I finally gave up after fruitless thinking.