adjective (often initial capital letters) Informal.
Origin of mickey mouse
adjective (sometimes not capitals) slang
Word Origin for Mickey Mouse
cartoon mouse character created 1928 by U.S. animator Walt Disney (1901-1966). As an adjective meaning "small and worthless" it dates from 1936, originally used especially of mediocre dance-band music, a put-down based on the type of tunes played as background in cartoon films.