of

On and off (মাঝে মাঝে) - It rained on and off all day.

Once an ant was very thirsty. He went to the pond to drink water.

Once in a blue moon = কালেভদ্রে - He comes to his village one in a blue moon

One day his wife became more furious than ever and began to insult Socrates.

One of my friends are a lawyer.   = One of my friends is a lawyer

one of my friends is a lawyer

One of the boys was absent yesterday. 

One should keep one's promise.

One should respect their parents.

One who practices engineering is called an engineer

One's health should be taken care.

Only Allah can help us.

Only Allah can help us. (Negative) =  None but Allah can help us. 

Open for all.  = Open to all.