I have suggested grammatically as a synonym of grammaticality. I believe that if the synonym is approved, re-tagging becomes unnecessary, but that may just be wishful thinking on my part. In any case, if the system will let you, please votevote on the synonym suggestion.
(It should go without saying that I believe the "grammatically" tag is a typo for "grammaticality".)
ETA: the synonym is now approved (thanks for the last vote, oerkelens!), and I was right: the system automatically re-tagged all the relevant questions.