Other forms: upended, upending, upends
To upend is to turn something on its end, or to overturn a plan. Upend the box, upend the table, upend the assumptions.
The literal sense is physical and exact. The figurative one is now much the commoner in writing: a finding that upends a theory turns it over rather than merely challenging it, and journalists reach for the word constantly.
1verbupendTo turn something on its end, or to overturn a plan.
“The children upended the toy box and tipped everything onto the floor.”
upend is an overturning.
From up- + end.
Etymology from Wiktionary, CC BY-SA