Sources

“A plain. O’Reilly gives “machair, a battle,” “maghair, ploughed land.” The ERSE machaire [maghery], a field, a plain, appears in some names (see Machermore), as in the Irish places Maghera and Maghery. Generally Machar may be taken to mean a level plain or field, the idea of ” battle ” being secondary (see Blair), from the place chosen for a battle, and of “beach,” from its level character, though in modern Gaelic it is “seldom used for

anything but a beach.”: Maxwell, Topography of Galloway

This name is derives from machair ‘plain’ and Galloway