Definition of Uncle Sam in US English:

Uncle Sam

proper noun

  • A personification of the federal government or citizens of the US, typically portrayed as a tall, thin, bearded man wearing a suit of red, white, and blue.

Origin

Early 19th century: said (from the time of the first recorded instances) to have arisen as an expansion of the letters US.

Pronunciation

Uncle Sam

/ˌəŋkəl ˈsæm//ˌəNGkəl ˈsam/