The word "headfast" means to be firmly anchored or fixed in place. Some synonyms for headfast include secure, steadfast, immovable, anchored, fixed, stable, strong, and unshakable. All of these words describe something that is firmly rooted or firmly held in place, whether it be a physical object or an abstract idea. They all suggest a sense of strength and permanence, conveying the message that something is not easily moved or altered. These synonyms can be useful when trying to convey a sense of solidity or permanence in your writing, and can help you to create a sense of stability or security in your work.