Lack, want, need, require are comparable when meaning to be without something, especially something essential or greatly to be desired.
Lack may imply either an absence or a shortage in the supply or amount of that something.
Want frequently adds to lack the implication of urgent necessity and may be difficult to distinguish from its sense connoting longing (see under DESIRE ).
For this reason need may be preferred when a clear connotation of urgent necessity is desirable <he cannot get the rest he needs > Need usually throws the emphasis on urgent necessity rather than on absence or shortage, though both implications are often present.
Require (see also DEMAND ) is often interchangeable with need but it may heighten the implication of urgent necessity.