The word "crenellate" means to provide battlements or loopholes in a castle or fortified wall. Some synonyms for "crenellate" would include fortify, embattle, or reinforce. These words suggest strengthening or bolstering a structure's defenses. Other synonyms include defend, secure, or protect, which emphasize the need for security and protection in a structure. Additionally, the word "fortress" could be used as a synonym, as it implies a strong and secure structure that is fortified against attack. In summary, there are several synonyms available for the word "crenellate," each of which can add a layer of meaning to a text or conversation.