The internet is well-supplied with useful, clear and sometimes witty explanations of what words mean. Some of these concentrate on distinguishing words with similar spelling or sound but different meaning. Most of these sites seem to be American. This could be because most wise English language wordsters are American or because most people making silly mistakes with English are American. Probably both, given the population.
Well, here's my contribution.
SPECTACULAR: Wearing spectacles or possessing spectacles - "She looks spectacular".
UNSPECTACULAR: Not needing or not having with one a pair of spectacles - "I am unable to read this document because I am unspectacular".
MALEFACTOR: The certain something that defines masculinity or distinguishes the male from the female; the male pudenda - "Those running shorts won't hide your malefactor".
DISEMBARK: Remove the outer covering from a tree - "The deer are disembarking the trees".
RATIONAL: Restricted to small portions - "Food is rational here".
RATIONALIST: Someone who believes in restricting things to small, defined portions - "If you were a rationalist you wouldn't eat so much".
RECTITUDE: Having a posterior - "The Bishop is a man of enormous rectitude".
ALLEGATION: A group of crocodile-like reptiles - "That allegation will not go away".
ALLEGORY: A suitably-prepared place to keep crocodile-like reptiles - "You don't find dragons in an allegory".
SPONTANEOUS COMBUSTION: Growing breasts naturally - "Anna was delighted she had spontaneously combusted".
FRIABLE: Suitable for cooking with oil - "Eggs are not friable unless you remove the shells".
MARINATE: Put something through a sailor - "Don't eat that - it's been marinated".
FASCINATE: Tie something up; become obsessed by uniforms, strong leadership and militaria - "Italians were fascinated by Mussolini".