[xoxoxoBruce]

A couple of these surprised me.

Data is a plural count noun not, standardly speaking, a mass noun.
Correct: "This datum supports the theory, but many of the other data refute it."

Disinterested means unbiasedand does not mean uninterested.
Correct: "The dispute should be resolved by a disinterested judge." / Why are you so uninterested in my story?

Enormity means extreme evil and does not mean enormousness.
Correct: The enormity of the terrorist bombing brought bystanders to tears. / The enormousness of the homework assignment required several hours of work.

Flounder means to flop around ineffectually and does not mean to founder or to sink to the bottom.
Correct: "The indecisive chairman floundered." / "The headstrong chairman foundered."

Fulsome means unctuous or excessively or insincerely complimentary and does not mean full or copious.
Correct: She didn't believe his fulsome love letter. / The bass guitar had a full sound.

Homogeneous is pronounced as homo-genius and "homogenous" is not a word but a corruption of homogenized.
Correct: The population was not homogeneous; it was a melting pot.

Hung means suspended and does not mean suspended from the neck until dead.
Correct: I hung the picture on my wall. / The prisoner was hanged.

Ironic means uncannily incongruent and does not mean inconvenientor unfortunate.
Correct: "It was ironic that I forgot my textbook on human memory." / It was unfortunate that I forgot my textbook the night before the quiz.

Irregardless is not a word but a portmanteau of regardless and irrespective.
Correct: Regardless of how you feel, it's objectively the wrong decision. / Everyone gets a vote, irrespective of their position.

Nonplussed means stunned, bewildered and does not mean bored, unimpressed.
Correct: "The market crash left the experts nonplussed." / "His market pitch left the investors unimpressed."

Practicable means easily put into practice and does not mean practical.
Correct: His French was practicable in his job, which required frequent trips to Paris./ Learning French before taking the job was a practical decision.
(my spellcheck refuses to accept practical, insisting on practicable, almost had me convinced I was wrong)

Protagonist means active character and does not mean proponent.
Correct: "Vito Corleone was the protagonist in 'The Godfather.' " / He is a proponent of solar energy.

Refute means to prove to be false and does not mean to allege to be false, to try to refute.
Correct: His work refuted the theory that the Earth was flat.

Reticent means shy, restrained and does not mean reluctant.
Correct: He was too reticent to ask her out. / "When rain threatens, fans are reluctant to buy tickets to the ballgame."

Urban legend means an intriguing and widely circulated but false story and does not mean someone who is legendary in a city.
Correct: "Alligators in the sewers is an urban legend." / Al Capone was a legendary gangster in Chicago.

To lie (intransitive: lies, lay, has lain) means to recline; to lay (transitive: lays, laid, has laid) means to set down; to lie (intransitive: lies, lied, has lied) means to fib.
Correct: He lies on the couch all day. / He lays a book upon the table. / He lies about what he does.