— upside-down , adj. — upside-downness , n.
1. with the upper part undermost.
2. in or into complete disorder; topsy-turvy: The burglars turned the house upside down.
[ 1300-50; re-formation (see UPSIDE) of ME upsedoun, earlier up so doun (see UP, SO 1 , DOWN 1 ; sense of so obscure) ]