Achilles heel

UK: /əˈkɪliːz/ US: /əˈkɪliz ˈhil/

WordReference Random House Learner's Dictionary of American English © 2025

A•chil•les heel /əˈkɪliz ˈhil/  n. [countable]

1. a weak or vulnerable spot: His generous nature was his Achilles heel in business dealings.

WordReference Random House Unabridged Dictionary of American English © 2025

Achil′les heel′, 

1. a portion, spot, area, or the like, that is especially or solely vulnerable:
   His Achilles heel is his quick temper.
   Also, Achil′les' heel′. 

• 1800–10

Collins Concise English Dictionary © HarperCollins Publishers::

Achilles heel noun

1. a small but fatal weakness