also: なくちゃ
expression
Used after the negative stem of a verb (ない-form minus ない) to mean 'without doing' or 'if not'. Often part of a conditional or negative obligation pattern.
朝ごはんを食べなくては、元気が出ない。
If I don't eat breakfast, I won't have any energy.
彼に会わなくては、何も始まらない。
Nothing will start unless I meet him.
expression
Abbreviation of なくてはいけない or なくてはならない. Used after the negative stem of a verb to express obligation. Very common in casual speech, especially as なくちゃ.
See also: なくてはいけない
もう行かなくちゃ。
I have to go now.
宿題をやらなくては。
I must do my homework.
Another full form of obligation, slightly more emphatic and formal than なくてはいけない.
Similar conditional meaning 'if not', but used with the plain negative form; often interchangeable with なくては in casual obligation.
From the negative continuative form なく (from ない) + particle て + topic particle は. The contracted form なくちゃ derives from なくては via regular sound change.