Weakness

wiktionary

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From Middle English weykenesse; equivalent to weak +‎ -ness.

etymonline

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weakness (n.)

c. 1300, "quality of being weak," from weak + -ness. Meaning "a disadvantage, vulnerability" is from 1590s. That of "self-indulgent fondness" is from 1712; meaning "thing for which one has an indulgent fondness" is from 1822.