This is the 13640th most frequent Russian word.
неинтересное
Uninteresting.
Here, 'неинтересная' is used as an adjective in its feminine singular form to describe the noun 'книжка' (book). It conveys that the speaker did not find the book engaging.
У меня есть книжка, которая показалась мне неинтересной.
I have a book that seemed uninteresting to me.
The word 'неинтересную' is used as an adjective in its feminine singular accusative form, modifying the noun 'история' (story). It indicates that the story lacks intriguing content.
Он рассказал неинтересную историю, и слушатели начали засыпать.
He told an uninteresting story, and the listeners began to fall asleep.
The word 'неинтересным' is an adjective in its masculine singular instrumental case, modifying 'фильм' (movie), declaring the speaker's disappointment about the movie's quality.