Don Pearce wrote:

The word "grammatic" isn't even in Merriam-Webster online. In
Dictionary Online it is given the meaning "of or pertaining to
grammar", which is not the usage we had here, which was of the correct
use of grammar - the word for which is grammatical.

The OED has no entry for grammatic.

Mine does, and that's just the Shorter OED.
When I'm feeling really pedantic I cycle seven miles to the public
library to consult the full 24 volume edition.

--
Eiron.