Idioms and Phrases

I would like to explain the meaning and example of the following ( and my fav.) idiom:

apple of discord
Meaning: anything causing trouble, discord, or jealousy.
Example: The run of two sisters for a single post has become an apple of discord, they are even fighting now.

Origion:
According to Greek mythology, the goddess Eris inscribed "to the fairest" and tossed in the midst of the feast of the gods at the wedding of Peleus and Thetis, thus sparking a vanity-fueled dispute among Hera, Athena and Aphrodite that eventually led to the Trojan War.

An idiom is the compact group of words that has a metaphorical meaning, basically because of its frequent usage.

An idiom's symbolic sense is quite different from the literal meaning or definition of the words of which it is made. There are a large number of Idioms and they used very commonly in all languages. There are approximately at least 25,000 idiomatic expressions in the English language.

Idioms in fact, evolve the language and they are the building blocks of a language and civilization as well they have great intensity to make a language interesting and dynamic.