Hard and fast ( বাঁধা ধরা ) There is no such hard and fast rule in this matter.
A rainy day ( দুর্দিন ) Everybody should save something for rainy day.
To and fro ( এদিন-ওদিক ) Being unable to make up his mind the man is walking to and fro.
At large ( স্বাধীন ) The anti-socials are still at large.
Fight shy ( এড়িয়ে চলা ) Why do you fight shy of your teacher.
A blessing in disguise ( বিপরীতে হিত ; প্রথমে খারাপ হিসেবে মনে হলেও পরবর্তীতে ভালো হয় ) Sam's motorcycle accident was a blessing in disguise because he got enough insurance money.