Birettas are a type of clerical hat that is traditionally worn by Christian clergy. Sometimes, it's helpful to use synonyms for the word "birettas" to add variety to your writing or to avoid repetition. Some potential synonyms for birettas might include "cap," "hat," "headdress," or "skullcap." Other possible options could include "vestment," "tassels," "edging," or "piping." Ultimately, the specific word you choose will depend on the context of your writing and the desired tone or style. However, by considering different synonyms for birettas, you can add nuance and depth to your language and create a more engaging, varied piece of writing.