Interjaculate is a rare and somewhat obscure word that refers to the act of interrupting a conversation by speaking unexpectedly. While there are not many direct synonyms for this word, there are a number of related expressions that convey a similar sense of sudden interruption or interjection. Some possible alternatives might include phrases like "cut in," "burst in," "insert oneself," "butt in," "pipe up," or simply "interrupt." Other similar words might include "intervene," "interpose," or "divert," which all suggest some kind of interruption or redirection of speech or conversation. Ultimately, the best synonym for interjaculate will depend on the specific context and tone of the conversation in question.