'Gritstone' definitions:

Definition of 'gritstone'

noun

A hard coarse-grained siliceous sandstone [syn: grit, gritrock, gritstone]

From: GCIDE

Gritrock \Grit"rock`\ (gr[i^]t"r[o^]k`), Gritstone \Grit"stone`\ (-st[=o]n`)n. (Geol.) See Grit, n., 4. [1913 Webster]

From: GCIDE

Grit \Grit\, n. [OE, greet, greot, sand, gravel, AS. gre['o]t grit, sant, dust; akin to OS griott, OFries. gret gravel, OHG. grioz, G. griess, Icel. grj[=o]t, and to E. groats, grout. See Groats, Grout, and cf. Grail gravel.]
1. Sand or gravel; rough, hard particles. [1913 Webster]
2. The coarse part of meal. [1913 Webster]
3. pl. Grain, esp. oats or wheat, hulled and coarsely ground; in high milling, fragments of cracked wheat smaller than groats. [1913 Webster]
4. (Geol.) A hard, coarse-grained siliceous sandstone; as, millstone grit; -- called also gritrock and gritstone. The name is also applied to a finer sharp-grained sandstone; as, grindstone grit. [1913 Webster]
5. Structure, as adapted to grind or sharpen; as, a hone of good grit. [1913 Webster]
6. Firmness of mind; invincible spirit; unyielding courage; fortitude. --C. Reade. --E. P. Whipple. [1913 Webster]