Wordology

Continuous and Continual - Continuous and continual are not the same, although they are similar. As Grammarist notes, things that happen without any interruption (like the flowing of a river) are continuous, while things that happen regularly with breaks in between (like bus departures) are continual.

Farther and Further - The difference between farther and further might be subtle, but it is important. Though both words mean "more distant," farther refers to physical distance, and further refers to figurative distance.

Allusion and Illusion - An allusion is a reference, most often one made in literature. An illusion, on the other hand, is a mirage or some other sort of deceptive appearance.

Evoke and Invoke - Evoke and invoke both come from the Latin word vocare for "call," so it makes sense that they are two of the most commonly confused words in the English language. These verbs are not interchangeable.
Evoke means "to call forth" and is typically used in reference to memories or emotions. Invoke, meanwhile, means "to call upon" and is most often heard in a court of law.