Real Dictionary

grout
uncountable noun: Grout is a thin mixture of sand, water, and cement or lime, which is used to fill in the spaces between tiles that are fixed to a wall.
verb: If you grout the tiles on a wall, you use grout to fill in the spaces between the tiles.

grout in American English
coarse meal
to fill or finish with grout
noun: a thin, coarse mortar poured into various narrow cavities, as masonry joints or rock fissures, to fill them and consolidate the adjoining objects into a solid mass

grout in British English
noun: a thin mortar for filling joints between tiles, masonry, etc
verb: to fill (joints) or finish (walls, etc) with grout