じゃなかった

じゃなかった is a colloquial expression used in Japanese to indicate that a statement or condition was not true in the past. This phrase is derived from the copula だ (da) and the negative じゃない (janai), combined with the past tense. For example, if you want to say 'It was not cold,' you would say '寒くなかった' (samukunakatta) which incorporates the negative form of cold (寒い) in its past tense.

It is important to note that じゃなかった is used in everyday conversation and is significantly less formal. In written form or in very polite conversation, using ではなかった (de wa nakatta) would be more appropriate. The usage of じゃなかった can be found across various contexts, making it an essential part of colloquial Japanese.