His heel. It has not been disclosed which one. (Maybe both?)
His heel because when his mother dipped him in the bath of immortality, she got every part exept his heel, because that's where she was holding onto Achilles , or he would've drowned. Thus, achille's weak spot was hit, and he died.
his weak spot
he has a weak spot for red heads
After bathing in the River Styx his "Achilles Heel" or weak spot was his underarm.
Achilles' heel was his weak spot thus the saying that someone's weakness is their "Achilles heel."
terds
In the crust the weak spot we have is the Magma Chamber. But, deep down to the mantle such weak zone is the Asthenosphere.
The weak spot of an alligator is it's somach
An "Achilles heel" is a person with a weak spot.
terds
His heel
his pride
Stomach