The idiom 'a snake in the grass' means-

- 'A snake in the grass' শব্দের অর্থ - a hidden enemy.

• A snake in the grass:
English Meaning: an unpleasant person who cannot be trusted, a secretly faithless friend.
Bangla Meaning: যাকে বিশ্বাস করা যায় না, গোপন শত্রু খুব ভয়ংকর জিনিস।
Sentence: A snake in the grass is very dangerous.

Source: Website Lecture.