This is the 762nd most frequent Hebrew word.
מקור
Source; origin.
In this sentence, "מקור" ('source') refers to the origin or primary reference from which the book's content is derived.
ספר זה נכתב על פי מקור עתיק.
This book was written based on an ancient source.
Here, "מקור" ('source') describes the place of origin or beginning of the river’s flow.
המקור של הנהר נמצא בהרים.
The source of the river is located in the mountains.
In this context, "מקור" ('beak') is used to denote the anatomical part of a bird's mouth.