ne·ces·si·ty 
/nɪˈsɛsəti/ noun
plural ne·ces·si·ties /nɪˈsɛsəti/ noun 1 [count] : something that you must have or do : something that is necessary
▪ Sunscreen is an absolute necessity for the beach. ▪ food, clothes, and other basic necessities ▪ Getting plenty of rest is a necessity. ▪ Without a car, living close to work is a necessity. ▪ All we took with us on our hiking trip were the bare necessities. ▪ Many families cannot even afford the basic/bare necessities of life. [=things that a person must have in order to survive] 2 [noncount] formal : the quality of being necessary — usually + of or for ▪ She talked about the necessity of having the right training. [=she said that having the right training is necessary] ▪ He questioned the necessity for the change. [=he questioned whether the change was necessary]
▪ Sunscreen is an absolute necessity for the beach. ▪ food, clothes, and other basic necessities ▪ Getting plenty of rest is a necessity. ▪ Without a car, living close to work is a necessity. ▪ All we took with us on our hiking trip were the bare necessities. ▪ Many families cannot even afford the basic/bare necessities of life. [=things that a person must have in order to survive]
by necessity or out of necessity
: because of conditions that cannot be changed
▪ The process is by necessity a slow one. [=the process is necessarily slow; the slowness of the process cannot be avoided] ▪ He works two jobs out of necessity. [=because it is necessary]
▪ The process is by necessity a slow one. [=the process is necessarily slow; the slowness of the process cannot be avoided] ▪ He works two jobs out of necessity. [=because it is necessary]
make a virtue (out) of necessity — see virtue
necessity is the mother of invention — see 1mother
of necessity
formal — used to say that something must happen or must be the way it is ▪ Further changes to the company will occur of necessity.
