[singular, uncountable] interest (in somebody/something) the feeling that you have when you want to know or learn more about somebody/something to feel/have/show/express (an) interest in something Do your parents take an interest in your friends? By that time I had lost (all) interest in the idea. I watched with interest. As a matter of interest (= I'd like to know), what time did the party finish? Just out of interest, how much did it cost?