Petty, stingy, or small-minded; used for someone who is cheap, mean, or sly about little things.
あんなにせこいことして、恥ずかしくないの？
Aren't you ashamed of doing something so petty?
飲み会で割り勘にしたら、彼だけせこくお釣りを細かく取った。
When we split the bill, he was stingy and kept insisting on getting his exact change.
せこい手を使って勝とうとしても、長続きはしない。
Even if you try to win by petty tricks, it won't last long.
Obsolete usage meaning poor or unskilled (historical; used by actors/performers in the Meiji era).
古い舞台評にはその役者を『せこい』と評する記述が見られる。
Old theater reviews sometimes describe that actor as 'sekoi' (poor/unskilled).