1
general::
Brag, boast, as in I don't believe he's ever shot even a duck, but he sure talks big about hunting. This colloquial idiom was first recorded in 1699.
American Heritage Idioms
2
general::
Phrase(s): talk big
to brag; to make grandiose statements. • She talks big but can’t produce anything. • He has some deep need to talk big, but it’s just talk—no action.
McGrawhill's American Idioms And Phrasal Verbs