There are over 100 words that can fit this:
Some choices for _as_er are:bastercasterdashereasierEasterfasterjaspermashermasterrashertastervasterwasherwaster
prairie
bellwort
rhyme
ladybirds, calyptras, kalyptras, capybaras
Some choices for _as_er are:bastercasterdashereasierEasterfasterjaspermashermasterrashertastervasterwasherwaster
A seven letter word starting with R and ending with O is risotto.
prairie
bellwort
rhyme
ladybirds, calyptras, kalyptras, capybaras
Crossers, trussers, dressers, pressers
Depends on the clue, could be Reno, Redo or Roto
Merriam-Webster's Official Scrabble Players Dictionary includes the 6 letter words deairs and kefirs. They are valid Scrabble words. Deairs means to remove air from. Kefirs means a fermented beverage made from cow's milk.
beware
France
Astore