If you are referring to human growth and development, growth would mean to increase in size, mass, substance, appearance, to essentially get larger. Humans start life as a single fertilized egg, called a zygote. This zygote starts the process of growth by undergoing cell division, many cell divisions within it's first week of existence. By this time, the zygote has divided so much it is now called an embryo, and about the third week, has many body systems already developing in place. By the end of the eighth week, the embryo has developed and grown enough to be called a fetus. The unborn child continues to grow and develop within the mother until around week forty, when it is born.
When you synthesize something, you are manufacturing something. In the case of growth, the predominant substance that is being manufactured is protein. It would be fair to say protein synthesis results in human growth and development. The synthesis of proteins occurs in the ribosomes, which are tiny cell organelles responsible for the synthesis and assembly of proteins for that cell.