noun
A person who habitually tells exaggerated stories or boasts. Often used in a mildly derogatory or teasing way. The term derives from ほら (tall tale) + 吹く (to blow), literally 'one who blows tall tales'.
See also: ほら
彼はほら吹きだから、話を半分くらいに聞いておいたほうがいいよ。
He's a braggart, so you'd better take what he says with a grain of salt.
あのほら吹きの言
Don't believe what that big talker says.
Compound of ほら (tall tale, from the image of blowing a conch shell to make a big sound) + 吹き (continuative form of 吹く 'to blow'). The metaphor is 'blowing' exaggerated stories.