瞒天大谎

enormous lie / whopper

day / sky / heaven

see 大夫[dai4 fu5]

big; large; great / older (than another person) / eldest (as in 大姐[da4 jie3]) / greatly; freely; fully / (dialect) father / (dialect) uncle (father's brother)

lies / to lie

to conceal from / to keep (sb) in the dark

gargantuan / as big as the sky / enormous