late 14c., "to go about, stroll," later (early 15c.) "roll from side to side, trundle," probably from Old French troller, a hunting term, "wander, to go in quest of game without purpose" (Modern French trôler), from a Germanic source (compare Old High German trollen "to walk with short steps"), from Proto-Germanic *truzlanan.
Sense of "sing in a full, rolling voice" (first attested 1570s) and that of "fish with a moving line" (c. 1600) both are extended technical uses from the general sense of "roll, trundle," the former from "sing in the manner of a catch or round," the latter perhaps confused with trail or trawl. Figurative sense of "to lure on as with a moving bait, entice, allure" is from 1560s. Meaning "to cruise in search of sexual encounters" is recorded from 1967, originally in homosexual slang.
The internet sense (everyone seems to have his own definition of it) seems to date to the late 1980s or early 1990s and the Newsgroups era, and the verbal use is perhaps older than the noun. It seems to combine troll (v.) in the "fish with a moving line" sense (itself confused with trawl) and troll (n.1) "troublesome imp supposed to live underground."
supernatural being in Scandinavian mythology and folklore, 1610s (with an isolated use mid-14c.), from Old Norse troll "giant being not of the human race, evil spirit, monster." Some speculate that it originally meant "creature that walks clumsily," and derives from Proto-Germanic *truzlan, from *truzlanan (see troll (v.)). But it seems to have been a general supernatural word, such as Swedish trolla "to charm, bewitch;" Old Norse trolldomr "witchcraft."
The old sagas tell of the troll-bull, a supernatural being in the form of a bull, as well as boar-trolls. There were troll-maidens, troll-wives, and troll-women; the trollman, a magician or wizard, and the troll-drum, used in Lappish magic rites. The word was popularized in literary English by 19c. antiquarians, but it has been current in the Shetlands and Orkneys since Viking times. The first record of the word in modern English is from a court document from the Shetlands, regarding a certain Catherine, who, among other things, was accused of "airt and pairt of witchcraft and sorcerie, in hanting and seeing the Trollis ryse out of the kyrk yeard of Hildiswick."
Originally conceived as a race of malevolent giants, they have suffered the same fate as the Celtic Danann and by 19c. were regarded by peasants in in Denmark and Sweden as dwarfs and imps supposed to live in caves or under the ground.
They are obliging and neighbourly; freely lending and borrowing, and elsewise keeping up a friendly intercourse with mankind. But they have a sad propensity to thieving, not only stealing provisions, but even women and children. [Thomas Keightley, "The Fairy Mythology," London, 1850]
"act of going round, repetition," 1705, from troll (v.). Meaning "song sung in a round" is from 1820.