"Of necessity" is a phrase that signifies the need for something to occur or be done. However, there are several synonyms that can be used in place of this phrase depending on the context of the sentence. For instance, "compulsory" conveys the notion of an action that is mandatory or required. "Essential" portrays something that is fundamental to the success of an endeavour or the achievement of a goal. "Indispensable" suggests that something is critical and cannot be dispensed with. Other synonyms for "of necessity" may include "inevitable," "imperative," "necessary," "mandatory," or "crucial," each of which portrays a sense of urgency and importance.