D defs.my
Entry 1 sense Webster, 1913

Upside down

/ŭp'-sīd' doun/ · Up·side down · IPA /ˌʌpsaɪd ˈdaʊn/
01 adv. in such a manner that the part normally pointed upward is pointed downward; same as upsidown and upsodown.
  1. 1.
    in such a manner that the part normally pointed upward is pointed downward; same as upsidown and upsodown. Also: upsidown, upsodown