This is the 5th most frequent Hindi word.
एक
"One"
In this sentence, 'एक' is used as an indefinite article denoting 'a single item' or 'one'.
मैंने एक किताब खरीदी।
I bought a book.
Here, 'एक' conveys a sense of unity or singularity among the group.
हम सब एक हैं।
We are all one.
In this sentence, 'एक' is used to specify an undefined or nonspecific instance of 'day'.