1Insistent, obstinate, persistent — describing a person or behavior that keeps pushing or repeating something to an annoying degree.
しつこい勧誘の電話に困っている。
I'm troubled by persistent sales calls.
彼はしつこく同じ質問を繰り返した。
He kept asking the same question over and over, insistently.
そんなにしつこく言わなくても、もうわかったよ。
You don't have to keep repeating it so insistently — I already understand.
この汚れはしつこくて、なかなか落ちない。
This stain is stubborn and just won't come out.
2Too rich, heavy, or cloying — describing a taste, smell, or richness (often fatty or oily) that feels overpowering.
このカレーは少し味がしつこい。
This curry's flavor is a bit too rich.
脂身の多い肉はしつこくて、たくさんは食べられない。
Fatty meat is so heavy that I can't eat much of it.
このケーキは甘さがしつこくて、一切れで十分だ。
This cake is so cloyingly sweet that one slice is enough.