Definition of ninnyhammer in English:

ninnyhammer

Pronunciation /ˈnɪnɪˌhamə/

noun

(also niniamer)
informal, dialect
  • A blockhead; a fool or braggart.

Origin

Late 16th century; earliest use found in Thomas Nashe (d. c1601), writer. Apparently from ninny (although this is first attested slightly later) + -hammer, of unknown origin.