achilles

Achilles' heel

Fig. a weak point or fault in someone or something otherwise perfect or excellent. (From the legend of Greek hero Achilles, who had only one vulnerable part of his body, his heel; as an infant his mother had held him by one heel to dip him in the River Styx to make him invulnerable.) He was very brave, but fear of spiders was his Achilles' heel.

See also: heel

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an Achilles' heel

a small fault in a person or system which might cause them to fail

Usage notes: Achilles was a man in Greek mythology (= an ancient set of stories) who was killed when he was injured on the heel. This was the only part of his body where he could be harmed.

As a team they're strong on attack but they have a weak defence that might prove to be their Achilles' heel. Vanity was his Achilles heel.

See also: heel