Ruthful "pitiable, lamentable, causing ruth" (c. 1200) has fallen from use since late 17c. except as a deliberate archaism, perhaps in part because it had a conflicting sense of "compassionate, tender-hearted, full of ruth." Ruthness "compassion, pity" (early 14c.) died even younger. Related: Ruthlessly; ruthlessness.
1540s, "having life, not dead," a shortening of alive (q.v.). From 1610s of fire, coal, etc., "burning, glowing;" 1640s of things, conditions, etc., "full of active power;" sense of "containing unspent energy or power" (live ammunition) is from 1799.
Meaning "in-person, not recorded" (of performance) is attested by 1917. Live wire is attested from 1890, "circuit through which an electric current is flowing;" figurative sense of "active person" is from 1903. Jocular real live "genuine" is from 1887. The older adjective is lively.
A GRIM RECORD — The death harvest of the "live wire" and "third rail" goes right on. It is not governed by seasons nor, qualified by time. It is the ubiquitous epidemic of electricity, defiant of doctors and ruthless as fate. [The Insurance Press, Aug. 22, 1900]
"dark sandstone," 1849, from brown (adj.) + stone (n.). It was quarried extensively from Triassic deposits in the U.S. Northeast and much-used there as a building stone. As "house or building fronted with brownstone" from 1932.
ONLY a few years ago to live in a brownstone front was a badge of distinction in Manhattan. Novelists always had their rich housed in brownstone fronts. There was magic in the name a quarter of a century ago. The brownstone front was the home of the merchant prince. The material had to be mined on the western plains of New Jersey and teamed and lightered to New York at a great cost in those days. O.O. Mclntyre writes there are blocks and blocks of them above Forty-second street, but of late they have fallen into decay. The advent of the luxurious apartment house put them in the shade. Now they are being torn down with ruthless abandon and the last shred of dignity has vanished. [The American Architect, Dec. 8, 1920]