necessary

The definition of necessary is being essential or required.

(adjective)

An example of necessary is a high school diploma or GED to obtain college admittance.

See necessary in Webster's New World College Dictionary

adjective

that cannot be dispensed with; essential; indispensable: the nutriments necessary to life
resulting from necessity; inevitable: a necessary result
1. that must be done; mandatory; not voluntary
2. not free to choose; compelled by circumstances: a necessary agent
inherent in the situation; undeniable; unavoidable from the premises
Archaic rendering some essential and intimate service

Origin: ME < L necessarius < necesse, unavoidable, necessary < ne-, not + cedere, to give way: see cede

a necessary thing; thing essential to life, some purpose, etc.: often used in pl.
Dialectal a privy or toilet
Law those things essential to maintaining a dependent or incompetent in comfort and well-being

See necessary in American Heritage Dictionary 4

adjective

Absolutely essential. See Synonyms at indispensable.
Needed to achieve a certain result or effect; requisite: the necessary tools.
a. Unavoidably determined by prior conditions or circumstances; inevitable: the necessary results of overindulgence.
b. Logically inevitable.
Required by obligation, compulsion, or convention: made the necessary apologies.