From the second edition (1989):
grit, n.2
(grɪt) Now only pl. and dial. Forms: α. sing. (rare) 1 grytt, 7 gritt, 8 grit. pl. 1 grytta, gretta, 3 gen. gruttene, 7 gritts, 7– grits. β. pl. 7 gurts, gert (see girt-brew), 9 girts. γ. pl. 6– greats, (7 greyts, 7–8 greets). [OE. grytt(e str. and wk. fem., usually in pl. grytta(n = MLG., Du. grutte fem., OHG. gruzzi (MHG., G. grütze):—OTeut. type *grutjâ, grutjôn-, f. Teut. root *greut-, graut-, grt-, whence also groats (a synonym, usually regarded as a mere variant, of this word), and grit n.1
This and the preceding n. seem to have mutually influenced each other in form, whence the γ forms here and the β forms of grit n.1]

1. Bran, chaff, mill-dust. Obs.

a700 Epinal Gloss. 823 Pullis, grytt. c1000 Ælfric Gloss. in Wr.-Wülcker 141/20 Apludes uel cantabra, hwæte gryttan. c1000 Sax. Leechd. II. 220 Þam mannum sceal man sellan‥niwe beren mela oððe grytta. a1100 Ags. Voc. in Wr.-Wülcker 330/33 Furfures, gretta. 11‥ Voc. ibid. 505/13 Polline, gryttes. a1225 Ancr. R. 186 Þis is Godes heste, þet him is muchele leouere þen þet tu ete gruttene bread, oðer werie herde here.

2. Oats that have been husked but not ground (or only coarsely); coarse oatmeal.
This is the general use of the word, but its application varies and has varied in Eng. dialects; in America it is applied to other kinds of grain. (See quots.)

1579 Langham Gard. Health (1633) 457 Otemeale Greyts. 1589 Cogan Haven Health vii. (1636) 31 Of the greats or groats‥boiled in water with salt, they make a kind of meat. 1601 Holland Pliny I. 559 In Gaule‥they have a kind of fourmentie corn or gurts‥named in their language Brance. 1615 Markham Eng. Housew. ii. viii. (1668) 178 The Greets or full Kernels will separate from the smaller oatmeal. a1661 Fuller Worthies, Linc. ii. (1662) 153 Gruel‥is wholsome Spoon-meat,‥Water is the Matter, Grits the Form thereof. 1686 Plot Staffordsh. 205 They are much smaller, without husk, and are indeed perfect gritts naturally, requiring no Mill to make them into Oatemeal. 1725 Bradley Fam. Dict. s.v. Oat meal, The bigger kind of Oat-Meal, which is call'd Greets, or Corn Oat-Meal. 1750 W. Ellis Country Housewife 206 Whole greets boiled in water till they burst, and then mixt with butter. 1796 H. Glasse Cookery xxi. 335 Grits [1747 (ed. 1) grotes] once cut does better than oatmeal. 1811 A. T. Thomson Lond. Disp. (1818) 68 Gruels, or decoctions of grits or of oatmeal, are excellent demulcents. 1847–78 Halliwell, Girts, oatmeal. Var. dial. 1884 Knight Dict. Mech. Suppl., Grits (Milling), cracked fragments of wheat smaller than groats. 1886 Syd. Soc. Lex. s.v., In America, fine hominy is called grits, and wheat prepared in the same way is likewise so designated. 1938 M. K. Rawlings Yearling iii. 27 Breakfast was on the table.‥ There were grits and gravy, hot cakes, and buttermilk. 1961 Encounter XVI. 20 Other eaters‥were forking up eggs and grits. 1969 New Yorker 10 May 32/1 We stopped for scrambled eggs and grits in a little town in Alabama.

3. attrib., as grit-gruel. See also girt-brew.

1844 T. Webster Encycl. Dom. Econ. 739 In the case of grits, this cuticle is entirely kept back, which accounts for the smoothness, as it is termed, of grit-gruel.