Boastful or grandiose talk; bragging or exaggerated claims (as in 'big talk' or braggadocio). Often literary or somewhat old-fashioned.
彼はいつも大言を並べるが、実際に行動することは少ない。
He always talks big, but rarely acts on it.
面接では大言を慎み、具体的な経験を話したほうが信用される。
At interviews it's better to avoid big talk and speak about concrete experiences to gain credibility.
その公約は大言壮語に終わってしまった。
That pledge ended up as mere bombast.