Grammar essentially a barrier, monarch for one abandoned Japanese (5,9)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

MA + DAM (barrier) + (Monarch) BUTTERFLY. But I don’t really understand how you get from “Grammar essentially” to MA. The letters are in there right enough, but so are AM or RA or MM … must be missing something. Ah, OK now I do. It is (gra)M(mar), which is the middle bit, + A + the rest. Silly me. Another clue I just bifd at the time. I will leave my original meanderings in place for posterity..