"gridiron, grated utensil for broiling over a fire," 1680s, from French gril, from Old French greil, alteration of graille "grill, grating, railings, fencing" (13c.), from Latin craticula "gridiron, small griddle," diminutive of cratis "wickerwork," perhaps from a suffixed form of PIE *kert- "to turn, entwine." Grill-room "lunchroom where steaks, chops, etc. are grilled to order" (1869) came to be used for "informal restaurant," hence grill as a short form in this sense (by 1910). In many instances, Modern English grill is a shortened form of grille, such as "chrome front of an automobile."
"to broil on a grill," 1660s, from grill (n.); figurative sense from 1842, and the specific (transitive) sense of "to subject to intense questioning" is first attested 1894. Related: Grilled; grilling.