grammatic vs idiomatic

grammatic

• grammatical 

idiomatic

• Resembling or characteristic of an idiom. 

• Pertaining or conforming to idiom, the natural mode of expression of a language. 

• Relating to parts or pieces which are written both within the natural physical limitations of the instrument and human body and, less so or less often, the styles of playing used on specific instruments. 

• Synonym of idiom