also: おおウソ
noun
outrageous lie; outright lie
A big, blatant lie; emphasizes the scale or shamelessness of the falsehood.
彼の話は大嘘だった。
His story was an outrageous lie.
そんなの大嘘に決まってるよ。
That's obviously a big fat lie.
Hiragana spelling, common in informal contexts.
嘘 is a general lie; 大嘘 specifically means a big, blatant lie.
Compound of 大 (big) + 嘘 (lie).