necessary (adj.)

 late 14c., necessarie, "needed, required; essential, indispensable; such as must be, that cannot be otherwise; not voluntary or governed by chance or free will," from Old French necessaire "necessary, urgent, compelling" (13c.), and directly from Latin necessarius "unavoidable, indispensable, necessary," from necesse "unavoidable, indispensable," originally "no backing away," from ne- "not" (from PIE root *ne-) + cedere "to withdraw, go away, yield" (from PIE root *ked- "to go, yield").