Be extremely knowledgeable or experienced; think one knows everything. Related expressions: know a thing or two (be competent), know it all (overconfident or ruefulness), know one's way around (genuine expertise).
Examples:
- Helen always knew all the answers, or thought she did.
Origin: Early 1900s for first term; later 1700s for know a thing or two; later 1800s for know it all; 1500s for know one's way around
Synonyms: know a thing or two, know it all, know one