The book was so heavy it sank in the water.
Meaning: This means that the book was too heavy to float on the water and it went down.
Choice of Words: The book is an object. Heavy means weighing a lot. Sank means went below the surface of a liquid and stayed there. Water is a liquid that falls from the sky as rain or forms rivers, lakes, and seas. When you put them together, it means the book was too heavy and went below the surface of the water.
Alternative Expressions
Related Expressions