WIDOW = woman 👩 whose spouse has died

WIDOWER = man 👨 whose spouse has died

DOWAGER = widow 👩 holding property 🏡🏢 from her dead spouse

Knowledge is an uncountable noun, so it is never used in the plural:

✗ Students don’t understand how to use these knowledges in real life.

✓ Students don’t understand how to use this knowledge in real life.

Knowledge is sometimes used with a, but only in the pattern a knowledge of something (or a good/deep/thorough etc knowledge of something):