unreasonable idea; illogical plan
Refers to a proposal, argument, or course of action that is forced, unreasonable, or doesn't hold up logically. Often used in discussions or negotiations.
I think that proposal is unreasonable.
illogical move (in shogi or go)
Original meaning; used in board games like shogi or go for a move that is strategically unsound or forced. Now less common than the general sense.
That move was illogical and was immediately countered.
彼の説明はどうも無理筋に感じる。
His explanation somehow feels illogical.
Compound of 無理 (muri, 'unreasonable') and 筋 (suji, 'line of reasoning' or 'move'). Originally used in board games, later extended to general illogical arguments or plans.