Achilles' heel

an Achilles'/Achilles heel AND
heel of Achilles (a weak point in a person or system; a weakness or vulnerability) — ахиллесова пята; слабое место; уязвимое место
Also an Achilles tendon.

...I think Frank's vanity is his Achilles' heel. — Я думаю, что тщеславие Франка — его ахиллесова пята.
...He played piano well, but his Achilles heel was rhythm. — Играл на пианино он хорошо, но слабым местом его был ритм.

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The Greek god, Achilles, was killed when he was injured on the heel. This was the only part of his body where he could be harmed. (Achilles was dipped in the River Styx by his mother to make him stronger; however, the only part of his body not submerged was his heel, which was his weak spot.) For thousands of years, this has been a metaphor for weakness.

Related Vocabulary

[уязвимое место]
[chink in the armor],
damaging weakness,
defect, failing, fatal flaw, flaw, foible, forlorn hope, frailty,
handicap,
susceptibility,
tender spot, vulnerability, vulnerable point,
weak link, weakness, weak point, weak side, weak spot