Main Entry:

up·side down

Pronunciation:

\ˈəp-ˌsīd-ˈdau̇n\

Function:

adverb

Etymology:

alteration of Middle English up so doun, from up + so + doun down

Date:

15th century

1 : in such a way that the upper and the lower parts are reversed in position 2 : in or into great disorder <turned their world upside down>

— upside–down adjective