What word is a noun weakness weakly weaker or weaken?

The Word weakness is the noun in the group; a Word for a lack of strength; a Word for a quality or feature considered as a disadvantage or fault.

The Word 'weaker' is the comparative form for the adjective 'weak' (weaker, weakest).

The Word 'weaken' is a verb (weaken, weakens, weakening, weakened).