信口雌黄

to speak off the cuff / to casually opine

letter / mail / CL:封[feng1] / to trust / to believe / to profess faith in / truthful / confidence / trust / at will / at random

to blurt sth out / to open one's mouth without thinking

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

female / Taiwan pr. [ci1]

orpiment / arsenic trisulfide As2S3 / make changes in writing / malign / criticize without grounds

yellow / pornographic / to fall through