The word "shakin" is a slang term that is often used to describe when someone is experiencing fear or anxiety. However, there are several other synonyms that can be used in place of this word to convey the same meaning. For instance, words like trembling, quivering, shuddering, and shaking can all be used to describe this state of mind. Similarly, words like quaking, shivering, and quavering can also be used to describe the physical and emotional effects of fear and anxiety. Ultimately, the choice of word will depend on the context of the sentence, but having a range of synonyms can add variety and nuance to your writing.