Xylophone
An eight letter word with three vowels using those letters is scavenge.Eight letter words with four vowels using those letters are agencies and envisage.
queueing
elephant
luminesce
starters, for starters
monsoons
queueing
Maybe eight letters- there is rhythms which has NO vowels and is seven lettersso changing it slightly to rhythmic makes eight letters.
sympathy
The Greeks added eight extra letters and modified the symbols for the letters.
Herein
Dopamine. I'm sure that there are others but I can't think of them at the moment.