'o' changes to 'ue' if the 'o' occurs in the accented syllable

absolver - to acquit
condolerse - to feel pity
conmover - to move, to touch
devolver algo - to give something back
disolver - to dissolve, to break up
doler - to hurt
envolver - to wrap up, to wind
llover - to rain
morder - to bite, to eat into
promover - to set up, to stir up
revolver - to turn around