“Side by side”, “day by day”... What is the meaning if I put same word linked with “by”? And is there any other phrase formed like this?
"By" indicates a continuation when it is used between two of the same word. For example, "side by side" means that objects or people are next to each other, which you can think of as "a side attached to another side". "Day by day" means that each day, something is progressing. "Hour by hour", "minute by minute" etc. have the same meaning, just a different time increment. Usually "by" is used between a time increment, like the previously mentioned examples.