Don't refresh page when enter key is pressed

you can either add following script at the end of body

<script>
        $("form").submit(function (e) {
            e.preventDefault();
            alert("call some function here");
        });
</script>

or you can just put your form tag like this

<form onsubmit="return false">

either way you will then have to write an onClick="SOMEFUNCTION()" to the input

also there is an error with an extra /button tag...remove that and instead use

<input type="button" class="btn btn-default" id="submit" value="Conjugate" />

note the ending slash

simply change your html:

<div id="forms" class="container">
        <form action="javascript:void(-1)">
            Enter your verb here in plain (dictionary) form:
            ....

jsfiddle here - works like charm