grout (n.) Look up grout at Dictionary.com
"thin, fluid mortar" used in joints of masonry and brickwork, 1580s, extended from sense "coarse porridge," perhaps from Old English gruta (plural) "coarse meal," from Proto-Germanic *grut-, from PIE root *ghreu- "to rub, grind" (see grit (n.)). As a verb from 1838. Related: grouted; grouting.