foible
noun
definition 1: a minor flaw or weakness in personality, character, or behavior.
example: Always forgetting our birthdays was just one of our dad’s foibles.
definition 2: a sword blade’s weaker part, from the middle to the point.
Examples from books
…You will then understand how slight an effort brought to bear on the foible of your opponent’s staff—in this case it will be somewhere
within two feet of the end–will suffice to turn aside the most vigorous thrust.
(Broad-Sword and Single-Stick, R.G. Allanson-Winn and C. Phillipps-Wolley, 1911)
Now this was Jim’s especial Foible,
He ran away when he was able,
And on this inauspicious day
He slipped his hand and ran away!
(Hilaire Belloc, “Jim, Who Ran Away From his Nurse and was Eaten by a Lion,” from Cautionary Tales for Children)
That Bismarck played on the Emperor’s foible for oppressed nationalities, in the case of Italy, is fairly certain.
(J. Holland Rose, The Development of the European Nations 1870-1914, 1915)