This is the 2600th most frequent Japanese word.
怪しい
Suspicious, doubtful, or strange.
怪しい is used to describe an individual whose behavior seems suspicious or doubtful.
その店の周りで怪しい人がうろついている。
A suspicious person is loitering around that shop.
怪しい conveys a sense of doubt or suspicion regarding the authenticity or truth of the price.
その宝石の値段は怪しいほど安い。
The price of that jewel is suspiciously low.
怪しい is expressing an unclear or dubious intention behind the smile.