This is the 419th most frequent Persian word.
تاثیر
Effect; impact.
In this context, "تاثیر" is used as a noun to signify the effect or impact that a subject (the book) has on someone (me).
این کتاب تاثیر عمیقی بر من گذاشت.
This book had a deep impact on me.
Here, "تاثیر" again acts as a noun to express the beneficial result that rain has on plant growth.
باران تاثیر مثبتی بر رشد گیاهان دارد.
Rain has a positive effect on the growth of plants.
In this sentence, "تاثیر" is employed as a noun to describe the aim of creating a beneficial or constructive outcome or influence.