"Need to know" is a phrase that signifies the importance of information that is essential for a particular purpose. Synonyms for "need to know" could include "essential information," "vital knowledge," "critical details," "indispensable facts," or "necessary intelligence." These words describe the essence of the phrase in different words as they express a similar sense of urgency that the information being referred to is crucial and cannot be overlooked. Other synonyms can also be "key data," "imperative specifics," "significant insights," or "relevant particulars." In brief, the synonyms convey the significance of information that is essential for decision-making, gaining knowledge, or accomplishing a task efficiently.