idioms

a Frankenstein’s monster (something that attacks or destroys the person who created it and cannot be controlled) Giving extra powers to the prince turned him into a Frankenstein’s monster, which is threatening to overthrow the king.     Frankenstein monster – English Vocabulary

    a fraidy-cat  US, informal (a fearful person, a coward) used mainly by children or to children Don’t be such a fraidy-cat; just jump into the water! Tom is a fraidy-cat; he is afraid of his own shadow.     fraidy cat – English Vocabulary

close to your heart (something important to you) Human welfare is a subject very close to my heart. (someone you love) I never knew that Ashley was so close to your heart; you two are really falling for each other. close to your heart – English Vocabulary

chicken hearted (fearful, cowardly) If you’re so chicken-hearted, you shouldn’t have come out with us. Don’t be so chicken-hearted. Let’s dive into the water from that diving board.   chicken hearted – English Vocabulary

change of heart (to change your opinion or feeling about something) She had a change of heart after learning the details of the deal. He was going to sell his car but had a change of heart at the last minute.   Change of heart – English Vocabulary