terrible luck; very bad luck
Primarily used for the worst fortune result on an omikuji (おみくじ) slip, but can also refer to extremely bad luck in general.
See also: おみくじ
I drew terrible luck on my fortune slip.
I was told my fortune this year is very bad.
大吉 is the best possible fortune on an omikuji, while 大凶 is the worst possible fortune.
Compound of 大 (great) and 凶 (bad luck). The exact historical derivation is uncertain, but the combination straightforwardly intensifies the meaning of 凶.