cannot do without; indispensable; absolutely necessary
Used when something is essential and cannot be omitted. Often follows a noun marked with が or は.
See also: なくてはいけない
Experience is indispensable for this job.
Attaches to the negative stem of a verb (ない-form minus ない) to express obligation. Colloquial contraction of なくてはいけない.
See also: なくてはいけない
Health is something you cannot do without.
I have to go now.
I must do my homework.
Contraction of なくてはいけない, from 無い (ない, 'not exist') + ては + いけない ('must not'). The ては contracts to ちゃ in casual speech.