Error executing a function in JS

I'm trying to run this function:

function createSlick(){  

    $(".slider").not('.slick-initialized').slick({
        centerMode: true,
        autoplay: true,
        dots: true,

        slidesToShow: 4,
        responsive: [{ 
            breakpoint: 768,
            settings: {
                dots: false,
                arrows: false,
                infinite: false,
                slidesToShow: 1,
                slidesToScroll: 1
            } 
        }]
    }); 
}

createSlick();

But you're giving this error:

  

Uncaught TypeError: $ (...). not (...). slick is not a function

Could someone help me solve it?