This is the 155th most frequent Urdu word.
ايک
"ايک" means "one" in English.
The word 'ايک' specifies a singular countable noun.
ايک سیب میز پر رکھا ہوا ہے۔
A single apple is placed on the table.
Here 'ايک' introduces an indefinite countable noun.
مجھے ايک کتاب پسند آئی۔
I liked a book.
In this sentence, 'ايک' is part of the phrase 'ايک دوسرے', which means 'each other'.