All words I've confused at one point or another. Explained poorly.
  1. Abstruse / Obtuse
    Hard to understand vs. unlikely to understand.
  2. Blond / Blonde and Brunet / Brunette
    Male/gender neutral vs. female. Does this distinction still exist? Corrected by an editor in an article I wrote once.
  3. Canvas / Canvass
    Canvas sail vs. canvass the neighborhood for the sale.
  4. Carat / Karat
    Diamonds vs. gold.
  5. Centrifugal / Centripetal
    Centrifugal force pushes out, centripetal force pulls in. Only confusing when you're spinning something heavy over your head, which is dangerous anyway so just don't do that and you'll be fine.
  6. Compliment / Complement
    I compliment your sweater, your sweater complements your eyes.
  7. Discreet / Discrete
    Circumspect vs. discontinuous.
  8. Divers / Diverse
    Several vs. different. Whatever, English.
  9. Hanged / Hung
    Hanged if you tried to kill them, hung otherwise. Aside: is this the only word whose conjugation depends on the intent of the subject?
  10. Heroin / Heroine
    Drugs vs. Buffy (which surprisingly was never a plot line).
  11. Innervate / Enervate
    Supply nerves to an organ vs. weaken. Note that neither of these means to awaken or enliven. Live and learn. ¯\_(ツ)_/¯
  12. Insure / Ensure
    Insure against losses vs. ensure no losses. Wait.
  13. Lightening / Lightning
    Make lighter vs. electrocuted by God.
  14. Mucus / Mucous
    Snot vs. snotty.
  15. Premise / Premises
    The basis of an argument vs. the base of an establishment.
  16. Rein / Reign
    Anybody can rein a horse but only the horse king reigns over the horses.
  17. Retch / Wretch
    Puking sound vs. the person making the puking sound.
  18. Silicone / Silicon
    Rubbery stuff vs. computer chip stuff.
  19. Weary / Wary
    Tired vs. untrusting.