What's the meaning of the phrase 'Achilles' heel'?
An Achilles' heel is a weak or vulnerable factor - especially one where all other components are strong.
What's the origin of the phrase 'Achilles' heel'?
The term 'Achilles' heel' comes from the myth of Achilles, who was said to have been dipped into the river Styx by his mother Thetis in order to make him invulnerable. His heel wasn't covered by the water and he was later killed by an arrow wound to his heel.
Although the legend is ancient, the phrase wasn't picked up in English until the 19th century. It is used as a metaphor for vulnerability, as in this early citation, an essay by Samuel Taylor Coleridge in The Friend; a literary, moral and political weekly paper, 1810:
"Ireland, that vulnerable heel of the British Achilles!"
The connection between Achilles and heels was called on when the tendon at the back of a human heel was named the Achilles' tendon.
See also, the Samuel Taylor Coleridge phrase - suspension of disbelief.