meaning：
any subject of disagreement and contention
the root of the trouble
a euphemism for a small matter that could leadto a bigger dispute
origin：
The Greek goddess of discord,Eris,became disgruntled after she was excluded
from the wedding of Peleusand Thetis.
In retaliation,she tossed a golden apple inscribed Kallisti('For the most beautiful one'),into the wedding party.Three goddesses claimed
the apple:Hera,Athena,
and Aphrodite.Paris of Troy was appointed to
select the recipient.He awarded the apple to Aphrodite,thus indirectly
causing the Trojan War.