The phrase "writ back" refers to a response or reply to a previous message or communication. There are several synonyms for this phrase that can be used interchangeably, including "reply," "respond," "answer," "retort," and "acknowledge." Each of these words conveys the same general meaning, but may be used in slightly different contexts or situations depending on the tone, formality, or level of urgency required. Other related terms that could be used instead of "writ back" might include "get in touch," "get back to," "reply to," or "correspond with." Ultimately, the choice of synonym will depend on the specific context and desired tone of the message being conveyed.