grey matter
gray matter
grey substance
gray substance
substantia grisea

It fell away to expose the gray substance, but she did not stop chopping.

Rudy took the screwdriver, put the point against the face of the gray substance, and leaned into it.

Matt held a sample of the gray substance in his hand.

The gray substance widened into a ring fastened to the ground, congealing in place.

It was made of a smooth, gray substance that showed no sign of age.

She felt composed of the grey substance too.

A gray, stone-like substance which he had seen before.

The clear cups filled not with water but with a thick, gray substance.

It is a loose, earthy substance, usually gray or bluish in color.

For awhile the grey substance only managed to move a few inches or so out of the hole.