Every curriculum publisher throws around the word vigor. I think this word is pretty meaningless in education now. I just wish curriculum developers showed you clear examples of materials that they consider challenging. Below is a picture of the words I'm teaching my 5th graders in our next word study unit. The bolded words will be on the spelling quiz at the end of the unit.
A few of my students are already strong spellers so they will be taught challenging words like acquiescence, effervescence, obsolescence, luminescence, reminiscense, verbose, grandiose, comatose, lachrymose, fructose, dispense, rescind, ascertain, oscillate, scintillation, and susceptible.
Many in the class will learn additional vocabulary during our MTSS block. These words are grouped by category as shown.
Knowledge of individual word meanings accounts for as much as 50–60 percent of the variance in reading comprehension.